JP2019189717A - Silver nanoparticle ink - Google Patents

Abstract

To provide a silver nanoparticle ink capable of preventing the generation of cracks in a dry coat.SOLUTION: A silver nanoparticle ink has: a dispersion medium containing water; silver nanoparticles having a dispersant, which is hydroxy acid or salt thereof, attached thereon, the silver nanoparticles being dispersed in the dispersion medium; and a water-soluble graft polymer dissolved in the dispersion medium while being released from the silver nanoparticles. The content of the water-soluble graft polymer is 3 pts.mass or more relative to the silver nanoparticles 100 pts.mass. Preferably, the dispersion medium contains a polyhydric alcohol.SELECTED DRAWING: None

Description

The present invention relates to a silver nanoparticle ink.

In recent years, printed electronics technology that forms extremely fine electronic circuits and devices by printing and firing conductive ink containing metal fine particles on a substrate has attracted attention. The fine metal particles used in the conductive ink are nanometer-sized particles that are much smaller than the conductive fillers in the conventional conductive paste, so they can be sintered at low temperatures due to the melting point drop unique to nanoparticles. In addition, there is a feature that high conductivity close to that of a metal foil can be realized. Silver nanoparticles are known as the metal fine particles used in such conductive ink.

Patent documents 1 and 2 are mentioned as literature which indicated the prior art about such conductive ink, for example.

Patent Document 1 discloses an aggregate of metal colloid particles containing metal nanoparticles (A) and a dispersant (B), wherein the dispersant (B) has a group having a nitrogen atom, a hydroxyl group, and a carboxyl group. There is disclosed a metal colloidal particle aggregate composed of an aggregating aid (B1) having at least one functional group selected from the group consisting of and a polymer dispersing agent (B2).

Patent Document 2 discloses a bonding agent for inorganic materials composed of metal colloid particles and a paste containing a dispersion medium of the metal colloid particles, wherein the metal colloid particles include metal nanoparticles (A) and the metal. The protective colloid (B) for dispersing the nanoparticles (A) is composed of an organic compound (B1) having a carboxyl group and a polymer dispersant (B2). A bonding agent for inorganic materials is disclosed.

JP 2010-202943 A JP 2010-150653 A

By the way, when the printed electronics technology is used to form a wiring by printing conductive ink on a resin base material, the base material is not provided with a receiving layer that absorbs the ink solvent. In the process of drying the conductive ink, the ink solvent is volatilized rapidly, so that the dispersion state of the nanoparticles in the conductive ink is changed, and the dry film may be broken. Further, when printing a thick film such as a wiring having a thickness of 1 μm or more, the shrinkage of the film in the drying process cannot be alleviated, and the dry film sometimes breaks.

This invention is made | formed in view of the said present condition, and it aims at providing the silver nanoparticle ink which can suppress generation | occurrence | production of the crack in a dry film.

As a result of various studies on methods for suppressing the occurrence of cracks in the dry coating of silver nanoparticle ink, the present inventors have determined that internal shrinkage stress that weakens the interparticle interaction during the drying process by using a certain amount of water-soluble graft polymer. The inventors have found that even when the dry film thickness of the inkjet printed wiring is 1 μm or more, the occurrence of cracks in the dry film can be prevented, and the present invention has been completed.

The silver nanoparticle ink of the present invention has a dispersion medium containing water, a dispersing agent which is a hydroxy acid or a salt thereof attached to the surface, and the silver nanoparticles dispersed in the dispersion medium and the silver nanoparticles are released from the silver nanoparticles. The water-soluble graft polymer dissolved in the dispersion medium is contained, and the water-soluble graft polymer is contained in an amount of 3 parts by mass or more with respect to 100 parts by mass of the silver nanoparticles.

The dispersion medium preferably contains a polyhydric alcohol. The water-soluble graft polymer preferably has an acid value and no base value.

According to the silver nanoparticle ink of the present invention, the occurrence of cracks in the dry film can be suppressed.

The silver nanoparticle ink of the present invention has a dispersion medium containing water, a dispersing agent which is a hydroxy acid or a salt thereof attached to the surface, and the silver nanoparticles dispersed in the dispersion medium and the silver nanoparticles are released from the silver nanoparticles. The water-soluble graft polymer dissolved in the dispersion medium is contained, and the water-soluble graft polymer is contained in an amount of 3 parts by mass or more with respect to 100 parts by mass of the silver nanoparticles.

(Dispersion medium)
The dispersion medium contained in the silver nanoparticle ink of the present invention disperses silver nanoparticles and contains water. Silver nanoparticle ink (water-based ink) using water as a dispersion medium is a highly polar ink before coating (before printing), but after forming a coating film, it changes to a hydrophobic film, that is, a nonpolar ink. Go. For this reason, aggregation of silver nanoparticles and a change in surface tension are likely to occur during the process of water evaporation, and the water-based ink has a greater change in coating film properties during the drying process than the organic solvent-based ink. From the above, the water-based ink originally has a tendency to easily generate cracks in the dried coating film, and the importance of preventing the cracks is high.

The water content in the silver nanoparticle ink of the present invention is preferably 20 to 50 mass%, more preferably 25 to 45 mass%. When the water content is 20% by mass or more, the dispersibility of the silver nanoparticles is sufficiently maintained. If the water content is 50% by mass or less, the content of other components such as silver nanoparticles will not be too low, so the viscosity of the silver nanoparticle ink will not be too low. Is easy to handle.

The dispersion medium may contain a smaller amount of organic solvent than water. Although the kind of organic solvent is not specifically limited, For example, a high boiling point solvent is suitable. As the high boiling point solvent, for example, polyhydric alcohol, glycol ether, butanol is used.

Examples of the polyhydric alcohol include glycerin, 1,3-propanediol, 1,2-propanediol (propylene glycol), 1,2,4-butanetriol, 1,2,6-hexanetriol, ethylene glycol, Examples include diethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methylpentane-2,4-diol and the like. These polyhydric alcohols may be used alone or in combination of two or more. Since the polyhydric alcohol that is compatible with water functions as a humectant, the nozzle clogging due to volatilization of the ink solvent can be suppressed, and the viscosity of the ink solvent can be adjusted to a viscosity that can be ejected by inkjet printing. The applicability of the nanoparticle ink (for example, the ejectability from the ink jet head) can be improved.

The content of the polyhydric alcohol in the silver nanoparticle ink of the present invention is preferably 5 to 35% by mass, more preferably 10 to 30% by mass. If the content of the polyhydric alcohol is 5% by mass or more, a moisturizing effect is sufficiently obtained, and the coating property of the silver nanoparticle ink is sufficiently enhanced. When the content of the polyhydric alcohol is 35% by mass or less, the viscosity of the silver nanoparticle ink does not become too high, and coating properties are sufficiently ensured.

Examples of the glycol ether include diethylene glycol monoisobutyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, ethylene glycol isopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol mono Butyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol mono 2-ethylhexyl ether, diethylene glycol mono 2-ethylhexyl Ether, ethylene glycol monoallyl ether, polyoxyethylene monoallyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, polyoxyalkylene monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether. These glycol ethers may be used alone or in combination of two or more.

Among the glycol ethers, diethylene glycol monoisobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol isopropyl ether, ethylene glycol monomethyl ether, and diethylene glycol monobutyl ether are preferable.

The content of glycol ether in the silver nanoparticle ink of the present invention is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass. When the content of glycol ether is 0.1% by mass or more, the wettability of the silver nanoparticle ink is sufficiently enhanced. If the content of glycol ether is 20% by mass or less, the viscosity of the silver nanoparticle ink does not become too high and the surface tension does not become too low, and coating properties (for example, ejection properties from an inkjet head) and drawing properties ( In particular, the drawability at the time of thin line drawing is sufficiently increased.

(Silver nanoparticles)
The silver nanoparticles are dispersed in the dispersion medium by attaching a dispersant which is a hydroxy acid or a salt thereof on the surface. The average particle diameter of the silver nanoparticles is preferably 1 to 400 nm, more preferably 1 to 70 nm. If the average particle diameter of the silver nanoparticles is 1 nm or more, a conductive film having excellent conductivity can be formed, and the production cost of the silver nanoparticles can be kept low. If the average particle diameter of the silver nanoparticles is 400 nm or less, the dispersion stability of the silver nanoparticles will hardly change over time.

The average particle diameter of the silver nanoparticles can be measured, for example, as a median diameter (D50) based on the particle diameter by volume using a dynamic light scattering method (Doppler scattered light analysis). Such a measurement can be performed by, for example, a dynamic light scattering particle size distribution measuring device “LB-550” manufactured by Horiba, Ltd.

The content of silver nanoparticles in the silver nanoparticle ink of the present invention is preferably 10 to 70% by mass, more preferably 20 to 60% by mass. When the content of silver nanoparticles is 10% by mass or more, a conductive film having sufficiently high conductivity can be formed. When the silver nanoparticle content is 70% by mass or less, the viscosity of the silver nanoparticle ink does not become too high, and coating properties (for example, ejection properties from an inkjet head) are sufficiently ensured.

The silver nanoparticle ink of the present invention may contain silver submicron particles having a submicron size that is larger than the silver nanoparticles (for example, the average particle size is 1 μm or less) in addition to the silver nanoparticles. Good. By using the nano-sized silver nanoparticles and the sub-micron sized silver sub-micron particles in combination, the silver nanoparticles have a melting point drop around the silver sub-micron particles, so that a good conductive path can be obtained.

The silver nanoparticle ink of the present invention may contain at least one kind of metal particles other than silver in addition to silver nanoparticles. By mix | blending metal particles other than silver, it becomes difficult to generate | occur | produce migration in the electrically conductive film formed with the silver nanoparticle ink of this invention. As the metal other than silver, a metal whose ionization row is noble more than hydrogen is preferable. Gold, copper, platinum, palladium, rhodium, iridium, osmium, ruthenium, and rhenium are preferable as the metal whose ionization column is more noble than hydrogen, and gold, copper, platinum, and palladium are more preferable. These metals may be used alone or in combination of two or more. The metal particles other than silver may be nano-sized particles or sub-micron-sized particles.

The dispersant attached to the silver nanoparticles is a hydroxy acid or a salt thereof. The hydroxy acid is not particularly limited as long as it has a COOH group and an OH group, but the number of COOH groups is preferably equal to or greater than the number of OH groups. According to such a dispersant, the dispersion stability of the silver nanoparticles is increased. Therefore, even if the content of silver nanoparticles is increased, aggregation is difficult and good dispersibility is maintained. In addition, according to such a dispersant, a conductive film having excellent conductivity can be formed even when fired at a low temperature of about 100 ° C. In particular, when a hydroxy acid having a total of three or more COOH groups and OH groups and having a number of COOH groups equal to or greater than the number of OH groups or a salt thereof is used as a dispersant, the dispersion stability of silver nanoparticles is improved. Since it increases more, the electrically conductive film which has the more excellent electroconductivity can be formed.

Examples of the dispersant include organic acids such as citric acid, malic acid, tartaric acid and glycolic acid; trisodium citrate, tripotassium citrate, trilithium citrate, monopotassium citrate, disodium hydrogen citrate, citric acid Ionic compounds such as potassium dihydrogen acid, disodium malate, disodium tartrate, potassium tartrate, sodium potassium tartrate, potassium hydrogen tartrate, sodium hydrogen tartrate, sodium glycolate; hydrates thereof and the like. Of these, trisodium citrate, tripotassium citrate, trilithium citrate, disodium malate, disodium tartrate, and hydrates thereof are preferable. These dispersants may be used alone or in combination of two or more.

The silver nanoparticles having the dispersant attached to the surface can be obtained, for example, by a method of reducing silver salt (silver ions) dispersed in a dispersion medium using the dispersant. That is, when the raw material aqueous solution containing the dispersant, the dispersion medium, and the silver salt is reduced, a colloidal solution containing silver nanoparticles in which the dispersant is present on at least a part of the surface can be obtained.

As the dispersion medium contained in the raw material aqueous solution, for example, an aqueous dispersion medium such as water or a water-soluble organic dispersion medium is preferably used. These aqueous dispersion media may be used alone or in combination of two or more. When the water-soluble organic dispersion medium is used by mixing with water, it is preferable to use, for example, 75% by volume or less of the water-soluble organic dispersion medium so that the resulting mixture is aqueous.

As the silver salt, a known reducible silver salt (or a hydrate thereof) can be used. For example, silver nitrate, silver sulfate, silver chloride, silver oxide, silver acetate, silver nitrite, silver chlorate, sulfide Examples thereof include silver salts such as silver (or hydrates thereof). These silver salts (or hydrates thereof) may be used alone or in combination of two or more. Further, these silver salts (or hydrates thereof) may be used in a state dissolved in an appropriate solvent, or may be used in a state dispersed in a solvent.

The method for reducing the silver salt in the raw material aqueous solution is not particularly limited, and examples thereof include a method using a reducing agent, a method of applying light (for example, ultraviolet rays), an electron beam, ultrasonic waves, heat, and the like. Among these, a method using a reducing agent is preferable from the viewpoint of ease.

The reducing agent is not particularly limited as long as it can be dissolved in the dispersion medium and reduce the silver salt (or hydrate thereof). For example, dimethylaminoethanol, methyldiethanolamine, triethanolamine, phenidone, Amine compounds such as hydrazine; hydrogen compounds such as sodium borohydride, hydrogen iodide, hydrogen gas; oxides such as carbon monoxide and sulfurous acid; ferrous sulfate, iron oxide, iron fumaroleate, iron lactate, iron oxalate Low-valent metal salts such as iron sulfide, tin acetate, tin chloride, tin diphosphate, tin oxalate, tin oxide, tin sulfate; formaldehyde, hydroquinone, pyrogallol, tannin, tannic acid, hydroxy acid, salicylic acid, D- And organic compounds such as glucose. Of these, tannic acid and hydroxy acid are preferable. These reducing agents may be used alone or in combination of two or more. When these reducing agents are used, the reduction reaction may be promoted by adding at least one of light and heat.

The tannic acid is not particularly limited as long as it is generally classified (collectively) as tannic acid, and includes, for example, gallotannic acid, pentaploid tannin and the like. The content of tannic acid is preferably 0.01 to 6 g, more preferably 0.02 to 1.5 g, per 1 g of monovalent silver ions. When the content of tannic acid is less than 0.01 g per gram of silver ions, the reduction reaction may be insufficient. When the content of tannic acid is more than 6 g per gram of silver ions, tannic acid may be excessively adsorbed and remain in the silver nanoparticle ink.

Examples of the method for preparing a colloidal solution containing silver nanoparticles by reducing the raw material aqueous solution with a reducing agent include the following methods. First, a silver salt solution is prepared by dissolving silver salt (or a hydrate thereof) in a dispersion medium such as pure water. Next, a colloidal solution is prepared by gradually dropping the silver salt solution into an aqueous solution in which the dispersant and the reducing agent are dissolved.

In the colloidal solution prepared in this way, in addition to silver nanoparticles, a reducing agent residue, a dispersing agent, and the like are present, and the electrolyte concentration of the entire solution tends to be high. In the colloidal liquid in such a state, the silver nanoparticles are agglomerated due to high electrical conductivity and are likely to precipitate. Therefore, it is preferable to remove this excess electrolyte by washing the colloidal solution.

As a method for washing the colloidal liquid, for example, a step of allowing the prepared colloidal liquid to stand for a certain period and removing the supernatant liquid, adding pure water and stirring, and further allowing to stand for a certain period of time to remove the supernatant liquid. A method that repeats several times is mentioned. Examples of other washing methods include a method of performing centrifugation instead of the above-described standing, a method of desalting with an ultrafiltration device, an ion exchange device, and the like. Of these, the desalting method is preferred. The desalted liquid may be concentrated as appropriate.

The content of silver nanoparticles in the colloidal liquid is preferably 1 to 70% by mass, more preferably 10 to 65% by mass. If the content of silver nanoparticles is 1% by mass or more, silver nanoparticles in an amount capable of realizing a conductive film having sufficient conductivity are secured in the conductive ink. If the content of silver nanoparticles is 70% by mass or less, the viscosity of the colloidal liquid will not be too high, and handling will be easy.

The content of the dispersant in the silver nanoparticles is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, and still more preferably 1 to 10% by mass. If content of a dispersing agent is 0.5 mass% or more, the storage stability of silver nanoparticles will fully improve. If content of a dispersing agent is 30 mass% or less, the electroconductivity of the electrically conductive film obtained will fully increase.

The colloidal liquid preferably has a weight loss of 10% by mass or less at 100 to 500 ° C. when thermogravimetric analysis is performed at a heating rate of 10 ° C./min with respect to the solid content. When the solid content is heated to 500 ° C., organic substances and the like are oxidatively decomposed, and most of them are gasified and disappear. Therefore, the weight loss when heated to 500 ° C. can substantially correspond to the content of organic matter in the solid content.

The greater the weight loss, the better the dispersion stability of the silver nanoparticles, but if the weight loss is too large, the organic matter remains as impurities in the silver nanoparticle ink, and the conductivity of the resulting conductive film is high. May decrease. In particular, in order to obtain a conductive film having excellent conductivity by heating (baking) at a low temperature of about 100 ° C., the weight loss is preferably 10% by mass or less. On the other hand, if the weight loss is too small, the dispersion stability of the silver nanoparticles is impaired. Therefore, the weight loss is preferably 0.01% by mass or more. The weight loss is more preferably 0.05 to 4.5% by mass.

The colloidal liquid may further contain a surfactant. In a multi-component solvent-based silver nanoparticle ink, roughening of the coating surface and unevenness of the solid content are likely to occur due to the difference in volatilization rate during drying. On the other hand, when a surfactant is added to the colloidal solution, these disadvantages are suppressed, and a silver nanoparticle ink capable of forming a uniform conductive film is obtained.

The surfactant is not particularly limited, and examples thereof include an anionic surfactant, a cationic surfactant, and a nonionic surfactant. Specific examples of such surfactants include fluorine surfactants, alkylbenzene sulfonates, and quaternary ammonium salts. From the viewpoint of obtaining an effect in a small amount, a fluorosurfactant is preferable.

(Water-soluble graft polymer)
The water-soluble graft polymer is dissolved in the dispersion medium while being released from the silver nanoparticles. In the present invention, a certain amount of water-soluble graft polymer can be used to reduce or alleviate internal shrinkage stress that weakens the interaction between silver nanoparticles during the drying process and partially generated tensile stress. Even when a dry film (conductive film) having a thickness of 1 μm or more is formed, the dry film can be prevented from cracking (cracking and checking). In addition, the crack which reaches | attains the base material of a film is called cracking (Cracking), and the shallow crack of the surface layer of a film is called checking (Checking).

The water-soluble graft polymer is free from the silver nanoparticles, and is different from the dispersing agent that is a hydroxy acid or a salt thereof attached to the silver nanoparticles in the silver nanoparticle ink of the present invention. . The difference in content between the two can be confirmed, for example, by separating the two when the silver nanoparticle ink of the present invention is subjected to ultrafiltration, microfiltration, or the like. Specifically, it is considered that the dispersant adhering to the silver nanoparticles remains on the filter membrane, the water-soluble graft polymer is contained in the filtrate, and both are separated.

There is no particular limitation on the method of releasing the water-soluble graft polymer from the silver nanoparticles and dissolving the polymer in a dispersion medium. However, silver nanoparticles having a hydroxy acid or a salt thereof attached to the surface were prepared. If the water-soluble graft polymer is added later, the above state can be easily formed. That is, instead of synthesizing silver nanoparticles in a system containing both a dispersant and a water-soluble graft polymer, silver nanoparticles are synthesized in a state where a dispersant which is a hydroxy acid or a salt thereof is added, The graft polymer may be added after the synthesis of the silver nanoparticles.

The water-soluble graft polymer is a copolymer having a structure in which a branch polymer constituting a side chain is bonded to a backbone polymer constituting a main chain and having a hydrophilic portion that is soluble in water. There is no particular limitation. As the water-soluble graft polymer, those having both a highly polar chain and a hydrophobic chain are suitable. Examples of the highly polar chain include a polyether chain and a molecular chain having a hydroxyl group. Examples of the hydrophobic chain include a polyacrylate chain, a fatty acid chain, a polyurethane chain, an alkyl chain, and an aromatic ring. In the water-based silver nanoparticle ink, a highly polar chain extends. On the other hand, in the coating film from which water has evaporated, the hydrophobic chain serves as a protective layer for solid particles. As such a water-soluble graft polymer, commercially available products can be used. For example, “SOLPERSE 44000” manufactured by Lubrizol and “DISPERBYK-190” manufactured by Big Chemie Japan can be used. .

Further, the water-soluble graft polymer preferably has an acid value and no base value. When the water-soluble graft polymer has a base number, the dispersibility of the silver nanoparticles may be insufficient. A preferable range of the acid value is 5 to 200 mgKOH / g.

The water-soluble graft polymer is contained in an amount of 3 parts by mass or more based on 100 parts by mass of the silver nanoparticles. When the content of the water-soluble graft polymer is less than 3 parts by mass with respect to 100 parts by mass of the silver nanoparticles, the effect of preventing cracking of the dry film cannot be obtained sufficiently. From the viewpoint of enhancing the effect of preventing cracking of the dry film, the water-soluble graft polymer is preferably contained in an amount of 3.5 parts by mass or more with respect to 100 parts by mass of the silver nanoparticles. Moreover, although the upper limit of content of the said water-soluble graft polymer is not specifically limited, From a viewpoint which prevents the electroconductivity of an electrically conductive film falling, it shall be 10 mass parts or less with respect to 100 mass parts of silver nanoparticles, for example. .

The viscosity of the silver nanoparticle ink of the present invention at 25 ° C. is preferably 3 to 20 cP. When the viscosity is in the range of 3 to 20 cP, an ink having excellent coating properties in ink jet printing can be obtained. The viscosity can be measured by, for example, a vibration type viscometer “VM-10A” manufactured by Seconic Corporation.

The surface tension of the silver nanoparticle ink of the present invention at 25 ° C. is preferably 20 to 40 mN / m. When the surface tension is 20 mN / m or more, the wettability of the silver nanoparticle ink with respect to the base material does not become too high, and the drawability (particularly drawability at the time of thin line drawing) is sufficiently secured. When the surface tension is 40 mN / m or less, the wettability of the silver nanoparticle ink with respect to the base material is not lowered too much, and problems such as interruption of the coating pattern are sufficiently prevented. The surface tension can be measured by, for example, a surface tension meter “CBVP-Z” manufactured by Kyowa Interface Science Co., Ltd.

The contact angle (static contact angle) of the silver nanoparticle ink of the present invention is preferably 15 to 40 ° with respect to the surface of the substrate to be coated. When the contact angle is 15 ° or more, the wettability of the conductive ink with respect to the substrate does not become too high, and the drawing property (particularly, drawing property at the time of thin line drawing) is sufficiently ensured. If the said contact angle is 40 degrees or less, the wettability of the silver nanoparticle ink with respect to a base material will not become low too much, and malfunctions, such as the pattern of a coating film being interrupted, are fully prevented. The contact angle can be measured, for example, with a contact angle meter “DropMaster DM-300” manufactured by Kyowa Interface Science Co., Ltd. in a state where a predetermined amount of silver nanoparticle ink is dropped on the surface of the substrate.

The method for producing the silver nanoparticle ink of the present invention is not particularly limited, and examples thereof include the following method. First, a colloidal solution containing silver nanoparticles having a hydroxy acid or a salt thereof adhering to the surface as a solid content is prepared. Next, the silver nanoparticle ink of the present invention is obtained by mixing the obtained colloid liquid, a dispersion medium such as water, a water-soluble graft polymer, and the optional components described above as necessary.

The silver nanoparticle ink of the present invention can be formed on a substrate and then baked to form a conductive film. 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 a material for the substrate, in addition to various ink absorbing materials (for example, paper, fabric, porous ceramics, etc.), non-ink absorbing materials may be used, and materials having excellent heat resistance are preferably used. It is done. Examples of non-ink-absorbing materials include polycarbonate (PC), ABS, AS, polypropylene (PP), polyethylene (PE), polyamide (PA), polyacetal (POM), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). ), Polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polystyrene (PS), polymethyl methacrylate (PMMA), polyphenylene ether (PPE), polysulfone (PSF), polyether sulfone (PES), polyamideimide ( PAI), polyetherimide (PEI), polyimide (PI), polyvinyl chloride (PVC), and other resins (engineering plastics and super engineering plastics). Here, the ink non-absorbing material means a material having no structure having an ink receiving function. A surface layer (primer layer) may be provided on the surface of the base material for the purpose of improving the adhesion with the conductive film, or a surface treatment such as a hydrophilic treatment may be performed. Examples of the surface treatment method include dry treatment such as corona treatment, plasma treatment, UV treatment, and electron beam treatment.

The above-mentioned application is a concept including a case where silver nanoparticle ink is applied in a planar shape and a case where it is applied (drawn) linearly. The shape of the coating film (conductive film) may be planar, linear, or a combination of these. The coating film (conductive film) may be a continuous pattern, a discontinuous pattern, or a combination of these.

The method for applying the silver nanoparticle ink of the present invention is not particularly limited. For example, the inkjet printing method, the screen printing method, the relief printing method, the intaglio printing method, the reverse printing method, the microcontact printing method, the dipping method, the spray method, Examples thereof include 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. Especially, it is preferable that the silver nanoparticle ink of this invention is an ink for inkjet printing.

When the coating film is baked, the bonding between the silver nanoparticles contained in the coating film is increased and sintered. The firing temperature of the coating film is preferably 150 ° C. or lower, more preferably 120 ° C. or lower, and still more preferably 100 ° C. or lower. According to the silver nanoparticle ink of the present invention, a conductive film having excellent conductivity can be formed even when baked at a temperature of 150 ° C. or lower. On the other hand, the lower limit of the firing temperature is not necessarily limited, and is a temperature at which a conductive film can be formed on the surface of the substrate, and water can be evaporated within a range that does not impair the effects of the present invention (partially It may be left, but it is preferable that all are removed). The firing time of the coating film is not particularly limited, and may be set as appropriate according to the firing temperature.

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

The film thickness of the said electrically conductive film is 0.1-5 micrometers, for example, Preferably it is 0.2-3 micrometers. The volume resistance value of the conductive film is preferably 1.1 × 10 ⁻⁴ Ω · cm or less, more preferably 1.0 × 10 ⁻⁴ Ω · cm or less, and further preferably 5.0 × 10 ⁻⁵ Ω · cm. cm or less.

EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples.

(Preparation of silver colloid aqueous solution)
First, 17 g of trisodium citrate dihydrate and 0.36 g of tannic acid were dissolved in 50 mL of water made alkaline by adding 3 mL of 10N-NaOH aqueous solution. Then, 3 mL of an aqueous solution containing 2 g of silver nitrate was added while stirring the obtained aqueous solution at room temperature (25 ° C.) to prepare an aqueous solution of silver colloidal particles. Next, desalting was repeated with respect to the obtained aqueous solution of silver colloid particles using an ultrafilter until the electric conductivity of the filtrate was 30 μS / cm or less. Then, when the obtained filtrate was centrifuged for 10 minutes, it was separated into a lower layer precipitate and an upper layer dispersion. Then, the upper layer dispersion was collected as a colloid liquid (silver colloid aqueous solution) containing silver nanoparticles having a dispersant attached to the surface.

The particle diameter of the silver colloid particles in the silver colloid aqueous solution was distributed in the range of 10 to 100 nm, and the median diameter (D50) was 25 nm. The particle size of the silver colloid particles was measured by the following method. First, several drops of an aqueous silver colloid solution were dropped into 10 mL of pure water and dispersed by shaking by hand to prepare a measurement sample. Next, 3 mL of the measurement sample was put into a cell of a dynamic light scattering particle size distribution measuring device “LB-550” manufactured by Horiba, Ltd., and the particle size was measured under the following conditions.
<Measurement conditions>
Data read count: 100 times Temperature inside cell holder: 25 ° C
<Display conditions>
Distribution form: Standard number of repetitions: 50 times Particle size standard: Volume-based refractive index of dispersoid: 0.200 to 3.900 (silver)
Refractive index of dispersion medium: 1.33 (water)
<System requirements>
Strength standard: Dynamic
Scattering intensity range upper limit: 10000.00
Scattering intensity range lower limit: 1.00

The content of the silver colloid particles in the silver colloid aqueous solution was 58% by mass as measured by a dry weight method. Further, the colloidal silver particles include a trisodium citrate dihydrate corresponding to a hydroxy acid having a COOH group and an OH group and having a number of COOH groups equal to or greater than the number of OH groups or a salt thereof. The content was 2 mass%.

(Example 1)
67.2 parts by mass of an aqueous silver colloid solution, 5.1 parts by mass of water, 5.0 parts by mass of diethylene glycol monoisobutyl ether, 10.1 parts by mass of 1,3-propanediol, 10.1 parts by mass of glycerin, 1.0 part by mass of water-soluble comb-type graft polymer A (manufactured by Lubrizol, “SOLSPERSE 44000”) and water-soluble comb-type graft polymer B (manufactured by Big Chemie Japan, “DISPERBYK- 190 ") 1.2 parts by mass (in terms of active ingredient) and 0.3 part by mass of a water-soluble homopolymer (manufactured by Nippon Shokubai Co., Ltd.," Polyvinylpyrrolidone K-30 ") A particle ink was produced.

(Example 2)
Except that the water-soluble comb-shaped graft polymer A (SOLSPERSE 44000) was not added, water was added so that the total amount was 100 parts by mass, and the silver nanoparticle ink of Example 2 was produced. did.

(Example 3)
The same as Example 1 except that the compounding amount of the water-soluble comb-type graft polymer A (SOLPERSE 44000) was changed to 1.5 parts by mass without adding the water-soluble comb-type graft polymer B (DISPERBYK-190). Then, water was added so that the total amount was 100 parts by mass, and the silver nanoparticle ink of Example 3 was produced.

(Comparative Example 1)
Without adding water-soluble comb-type graft polymer A (SOLPERSE 44000) and water-soluble comb-type graft polymer B (DISPERBYK-190), the amount of water-soluble homopolymer (polyvinylpyrrolidone K-30) is 2.3 parts by mass. Except for the change, water was added so that the total amount was 100 parts by mass in the same manner as in Example 1 to produce a silver nanoparticle ink of Comparative Example 1.

(Comparative Example 2)
Comparative Example in which water was added to a total amount of 100 parts by mass in the same manner as in Example 2 except that the amount of water-soluble comb-type graft polymer B (DISPERBYK-190) was changed to 0.9 parts by mass. Two silver nanoparticle inks were produced.

(Comparative Example 3)
The same as Comparative Example 2 except that the water-soluble comb-type graft polymer B (DISPERBYK-190) was not added and the blending amount of the water-soluble comb-type graft polymer A (SOLPERSE 44000) was changed to 0.9 parts by mass. Then, water was added so that the total amount was 100 parts by mass, and the silver nanoparticle ink of Comparative Example 3 was produced.

[Evaluation test]
Using the silver nanoparticle ink prepared in Examples and Comparative Examples, the following physical property evaluation and printed matter evaluation were performed.

(1) Viscosity Using a vibration viscometer “VM-10A” manufactured by Seconic Co., Ltd., the viscosity of the silver nanoparticle ink at 25 ° C. was measured.

(2) Surface tension The surface tension at 25 ° C. of the silver nanoparticle ink was measured using a surface tension meter “CBVP-Z” manufactured by Kyowa Interface Science Co., Ltd.

(3) A sample obtained by diluting the dispersible silver nanoparticle ink twice with water was allowed to stand at room temperature for 1 day, and then the presence or absence of precipitation and the state of the supernatant were visually observed. The dispersibility of the silver nanoparticle ink was evaluated according to the following criteria.
O: Almost no sediment was observed under the container.
Δ: A small amount of sediment was observed under the container.
X: There was a clear difference in concentration between the top and bottom of the container, and sediment was clearly observed.

(4) A sample obtained by diluting dilutable silver nanoparticle ink 100 times with water was allowed to stand at room temperature for 1 week, and then the dispersibility was visually confirmed. The dilutability of the silver nanoparticle ink was evaluated according to the following criteria.
A: Aggregation and silver mirror were not observed, and silver nanoparticles were dispersed.
Δ: Aggregation and silver mirror were observed in part.
X: Aggregation and precipitation occurred.
The silver mirror refers to a state in which a reflection such as gloss occurs because most of the particles are dispersed, but some of the particles adhere to the wall of the sample tube, and the precipitation occurs at the bottom of the sample tube. Indicates a state in which the liquid settles and the liquid and particles are separated.

(5) After applying the silver nanoparticle ink on a slide glass having a volume resistance value of 25 mm × 25 mm by a spin coating method at a rotation speed of 2000 rpm and a rotation time of 15 seconds, the condition is 120 ° C. for 30 minutes in a gear oven. Was heated to sinter the silver nanoparticle ink to form a conductive coating. The surface resistance value of this conductive film was measured with a resistivity meter “Loresta GP MCP-T610” manufactured by Mitsubishi Chemical Analytech Co., Ltd. to obtain a surface resistance value. Next, the thickness of the conductive film was measured with a laser microscope “VK-X150” manufactured by Keyence Corporation. Based on the following formula, the volume resistance value was calculated from the surface resistance value and the thickness of the conductive coating.
Formula: Volume resistance (Ω · cm) = Surface resistance (Ω / □) × Conductive film thickness (μm) / 10000

(Sample preparation for printed matter evaluation)
Samples used for the evaluation of crack resistance of the following (6) dry coating film and (7) adhesion were formed by the following method. First, the silver nanoparticle ink prepared in Examples and Comparative Examples was filtered with a syringe filter having a pore diameter of 0.45 μm and applied onto the surface of a polycarbonate (PC) substrate to form a coating film. The silver nanoparticle ink was applied with an ink droplet of 10 pL using an inkjet printer “Dimatix DMP-2831” and a cartridge “DMC-11610” manufactured by FUJIFILM Corporation. Then, the formed coating film was baked for 4 hours in a gear oven set at 120 ° C. to form a conductive film (printed wiring).

(6) The number of cracks contained in the entire linear pattern, using a laser microscope “VK-X150” manufactured by Keyence Co., Ltd., for the conductive film formed in a linear pattern having a crack resistance width of 1 mm and a length of 15 mm. It was confirmed. Judgment criteria were as follows.
◯: Number of cracks is 0 Δ: Number of cracks is 1 to 10 ×: Number of cracks is 11 or more

(7) Based on the adhesion pull-off method, cellophane (registered trademark) was applied to the conductive film (printed wiring) on the PC substrate, and the peeled state of the printed wiring after peeling the cellotape (registered trademark) was confirmed. . For each silver nanoparticle ink of Examples and Comparative Examples, 5 print samples were prepared on which printed wiring with a linear pattern having a width of 1 mm and a length of 15 mm was formed. In addition, the cello tape (registered trademark) was strongly rubbed against the printed wiring and strongly peeled off in the vertical direction. The determination criteria were as follows, and it was determined that peeling occurred in the printed sample not only when all the printed wiring was peeled off but also when the printed wiring was partially peeled off.
◯: The number of print samples where peeling occurred 0 to 1 Δ: The number of printing samples where peeling occurred 2 to 3 ×: The number of printing samples where peeling occurred 4-5

For the examples and comparative examples, the composition of the silver nanoparticle ink and the results of the evaluation test are shown in Table 1 below.

Examples 1 to 3 are superior to Comparative Examples 1 to 3 in crack resistance. Among them, Example 1 in which the amount of the water-soluble graft polymer added to the silver nanoparticles is the largest is more than Examples 2 and 3. Excellent crack resistance. Moreover, the crack resistance of Example 2 to which only the water-soluble comb-type graft polymer B (DISPERBYK-190) was added and Example 3 to which only the water-soluble comb-type graft polymer A (SOLPERSE 44000) was added are equivalent. There was no difference in crack resistance depending on the type of water-soluble comb graft polymer.

In Comparative Example 1, the amount of the water-soluble homopolymer was increased without adding the water-soluble graft polymer, but good crack resistance was not obtained. Further, in Comparative Examples 2 and 3, about 2.3 parts by mass of the water-soluble graft polymer was added to 100 parts by mass of the silver nanoparticles, but good crack resistance was not obtained.

In Examples 1 to 3, good results were obtained in terms of viscosity, surface tension, dispersibility, dilution, volume resistance, and adhesion.

Claims (3)

A dispersion medium containing water;
Dispersing agent which is a hydroxy acid or a salt thereof adheres to the surface, and silver nanoparticles dispersed in the dispersion medium,
Containing a water-soluble graft polymer dissolved in the dispersion medium while being released from the silver nanoparticles,
The silver nanoparticle ink comprising 3 parts by mass or more of the water-soluble graft polymer with respect to 100 parts by mass of the silver nanoparticles. The silver nanoparticle ink according to claim 1, wherein the dispersion medium contains a polyhydric alcohol. The silver nanoparticle ink according to claim 1 or 2, wherein the water-soluble graft polymer has an acid value and no base value.