Conductive film and method for forming the same

Abstract

The present invention relates to a conductive film having excellent adhesion to a substrate. The conductive film is formed on a substrate, and contains a photoreduction sinter of a composition containing cuprous oxide particles and a binder resin. An unsintered layer containing cuprous oxide particles and a binder resin, which have not been photoreduced, is formed between the substrate and the conductive film. The carbon mole fraction in the molecules of the binder resin is 0.15% to 0.9%, and the oxygen mole fraction is 0.03% to 0.2%.

Description

Technical Field

[0001] This invention relates to conductive films and methods for forming conductive films.

[0002] ‎ Background Technology

[0003] With the widespread use of IC tags and the like, technologies for forming conductive films are being developed not only on polyethylene terephthalate (PET) films but also on materials such as paper. Especially with paper and other substrates, to minimize the impact of heat on the substrate, it is necessary to form the conductive film at a lower temperature with a shorter heating time, and to achieve the same conductivity as when forming a conductive film at a higher temperature. One known method for forming such a conductive film is to coat a substrate with a light-sintering composition comprising cuprous oxide particles, a solvent, and a binder resin to form a coating film, and then irradiate the coating film with light, thereby reducing the cuprous oxide particles in the coating film to copper, thus forming a conductive film (see Patent Documents 1 and 2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-149360

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-200912 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, the conductive film formed by the technology described in Patent Documents 1 and 2 has the problem of insufficient adhesion to the substrate.

[0010] Therefore, the purpose of this invention is to provide a conductive film with excellent adhesion to a substrate and a method for forming the same.

[0011] Technical means to solve the problem

[0012] In view of the above-mentioned actual situation, the inventors of the present invention have repeatedly conducted in-depth research and found that: by providing an unsintered layer containing cuprous oxide particles that have not been photo-reduced and remain and a specific adhesive resin between the conductive film containing a composition comprising cuprous oxide particles and a specific adhesive resin and the substrate, the above-mentioned problems can be solved, thereby completing the present invention.

[0013] That is, the present invention relates to a conductive film, wherein the conductive film is formed on a substrate, the conductive film contains a photoreduction sintered material comprising a composition comprising cuprous oxide particles and a binder resin, and an unsintered layer comprising cuprous oxide particles that have not been photoreduced and remain and binder resin is formed between the substrate and the conductive film, wherein the binder resin has a carbon molar fraction of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2%.

[0014] Furthermore, the present invention relates to a method for forming a conductive film, wherein the method is a method for forming a conductive film on a substrate, the method comprising: a step of coating a composition comprising cuprous oxide particles and an adhesive resin onto the substrate to form a coating film; and a step of irradiating the coating film with light to photo-reduc and sinter the cuprous oxide particles in the coating film to form a conductive film, and forming an unsintered layer comprising cuprous oxide particles that have not been photo-reduced and remain and the adhesive resin between the substrate and the conductive film, wherein the carbon molar fraction in the adhesive resin molecules is 0.15% to 0.9%, and the oxygen molar fraction is 0.03% to 0.2%.

[0015] Invention Effects

[0016] According to the present invention, a conductive film with excellent adhesion to a substrate and a method thereof can be provided. Attached Figure Description

[0017] Figure 1 The images are SEM images of the cross-section of the conductive film formed on the substrate in Example 2 and EDS elemental mapping images of copper, oxygen and carbon. Detailed Implementation

[0018] The conductive film according to one embodiment of the present invention is characterized by having a photoreduction sintered material containing a composition comprising cuprous oxide particles and a binder resin formed on a substrate, and an unsintered layer containing cuprous oxide particles that have not been photoreduced and remain, and the binder resin, formed between the substrate and the conductive film. The binder resin has a carbon molar fraction of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2%. In the conductive film of one embodiment of the present invention, by providing a predetermined unsintered layer between the substrate and the conductive film, excellent conductivity can be ensured, and the binder resin in the unsintered layer can exhibit an adhesive effect, thereby improving the adhesion between the substrate and the conductive film. As described above, the unsintered layer contains cuprous oxide particles that have not been photoreduced and remain, and the binder resin, but it may also contain a small amount of copper generated by the photoreduction of some of the cuprous oxide particles. From the viewpoint of improving adhesion to various substrates while ensuring excellent conductivity, the ratio of the thickness of the conductive film after compression treatment to the thickness of the unsintered layer is preferably 10:90 to 98:2, more preferably 20:80 to 90:10. When the ratio of the thickness of the conductive film to the thickness of the unsintered layer is less than 10:90, the ratio of the conductive film decreases, making it difficult to obtain sufficient conductivity. When the ratio of the thickness of the conductive film to the thickness of the unsintered layer is greater than 98:2, the ratio of the conductive film increases, potentially making it difficult to obtain sufficient adhesion using the unsintered layer. It should be noted that, in one embodiment of the present invention, the cross-section of the conductive film formed on the substrate after compression treatment was analyzed by EDS elemental mapping of copper, oxygen, and carbon using a scanning electron microscope (SEM) to determine the boundary between the substrate and the unsintered layer and the boundary between the conductive film and the unsintered layer. The thickest parts of the conductive film and the unsintered layer are determined from these two boundaries and are respectively taken as the thicknesses of the conductive film and the unsintered layer.

[0019] In one embodiment of the present invention, the cuprous oxide particles used are not particularly limited; any cuprous oxide particles that can be reduced to copper by light irradiation are acceptable, and commercially available products can also be used. Furthermore, the manufacturing method of the cuprous oxide particles is not particularly limited. The shape of the cuprous oxide particles is not particularly limited; they can be any shape, such as spherical, polyhedral, or irregular. From the viewpoint of excellent operability and photosintering properties, the average primary particle size of the cuprous oxide particles is preferably 1 nm to 2000 nm, more preferably 15 nm to 500 nm, and even more preferably 30 nm to 300 nm. It should be noted that the average primary particle size of the cuprous oxide particles in one embodiment of the present invention is obtained by measuring the primary particle size of 50 randomly selected cuprous oxide particles in an image observed using a scanning electron microscope (SEM), and then arithmetically averaging their values.

[0020] From the viewpoint of suppressing the increase in viscosity of the composition and forming a conductive film of sufficient thickness, it is preferable that the composition contains 3% to 95% by mass of cuprous oxide particles, and more preferably 5% to 85% by mass of cuprous oxide particles.

[0021] From the viewpoint of easily forming a conductive film with few defects and uniformity, the cuprous oxide particles used in one embodiment of the present invention preferably contain at least one additive element selected from tin, manganese, vanadium, cerium, and silver. The preferred content of the additive element varies depending on the type of additive element, but is acceptable as long as it is in the range of 1 ppm to 30,000 ppm. When the additive element is tin, from the viewpoint of controlling tin ion solubility and cuprous oxide particle size, its content is preferably 1 ppm to 30,000 ppm, more preferably 10 ppm to 10,000 ppm, and even more preferably 150 ppm to 3,000 ppm. When the additive element is manganese, from the viewpoint of controlling manganese ion solubility and cuprous oxide particle size, its content is preferably 10 ppm to 20,000 ppm, more preferably 30 ppm to 10,000 ppm, and even more preferably 100 ppm to 8,000 ppm. When vanadium is added, from the viewpoint of controlling vanadium ion solubility and cuprous oxide particle size, its content is preferably 10 ppm to 20,000 ppm, more preferably 30 ppm to 10,000 ppm, and even more preferably 100 ppm to 8,000 ppm. When cerium is added, from the viewpoint of controlling cerium ion solubility and cuprous oxide particle size, its content is preferably 10 ppm to 30,000 ppm, more preferably 30 ppm to 20,000 ppm, and even more preferably 10 ppm to 10,000 ppm. When silver is added, from the viewpoint of controlling silver ion solubility and cuprous oxide particle size, its content is preferably 1 ppm to 30,000 ppm, more preferably 5 ppm to 20,000 ppm, and even more preferably 10 ppm to 10,000 ppm. Among these added elements, tin is preferred from the viewpoint of low melting point and low electrical resistance. It should be noted that, in this invention, the content of the added element in the cuprous oxide particles is the value obtained by dissolving 1g of cuprous oxide in 10ml of concentrated hydrochloric acid and measuring the solution using an ICP luminescence analyzer (ICPS-8100 manufactured by Shimadzu Corporation).

[0022] The aforementioned cuprous oxide particles containing added elements can be manufactured, for example, by mixing an aqueous solution containing copper ions and at least one added ion selected from divalent tin ions, divalent manganese ions, tetravalent vanadium ions, trivalent cerium ions, and monovalent silver ions with an alkaline solution to generate copper hydroxide, followed by the addition of a reducing agent to reduce and precipitate the cuprous oxide particles. During the generation of copper hydroxide and the reduction and precipitation of cuprous oxide particles, it is preferable to stir the reaction solution to ensure uniformity. The average primary particle size of the cuprous oxide particles can be adjusted using conditions such as the concentration of added ions during the manufacture of the cuprous oxide particles and the mixing temperature of the copper ion-containing aqueous solution and the alkaline solution.

[0023] As a source of copper ions in aqueous solutions, inorganic copper compounds such as copper chloride, copper sulfate, copper nitrate, copper cyanide, copper thiocyanate, copper fluoride, copper bromide, copper iodide, copper carbonate, copper phosphate, copper fluoride-borate, copper hydroxide, and copper pyrophosphate, as well as organic copper compounds such as copper acetate and copper lactate, and their hydrates, can be used. These copper ion sources can be used alone or in combination of two or more. Among these copper ion sources, copper chloride and copper sulfate are preferred from the viewpoint of high solubility in water and low cost. From the viewpoint of reaction efficiency, the copper ion concentration in the aqueous solution is preferably 0.1 mol / L to 2 mol / L.

[0024] The addition of at least one ion selected from divalent tin ions, divalent manganese ions, trivalent and tetravalent vanadium ions, trivalent cerium ions, and monovalent silver ions in the aqueous solution not only reduces the average primary particle size of the obtained cuprous oxide particles but also improves the reducing sintering properties of copper. As a divalent tin ion source, inorganic tin compounds such as tin(II) chloride, tin(II) sulfate, tin(II) oxide, tin(II) fluoride, tin(II) bromide, and tin(II) iodide, as well as organotin compounds such as tin(II) acetate, and their hydrates, can be used. These can be used alone or in combination of two or more. As a divalent manganese ion source, inorganic manganese compounds such as manganese(II) sulfate, manganese(II) chloride, and manganese(II) nitrate, as well as organomanganese compounds such as manganese(II) acetate, and their hydrates, can be used. These can be used alone or in combination of two or more. As a tetravalent vanadium ion source, inorganic vanadium compounds such as vanadium oxysulfate (IV), vanadium tetrachloride (IV), vanadium hydrochloride (IV), vanadium chloride (III), vanadium oxide (III), and vanadium oxide (IV), as well as organic vanadium compounds such as vanadium tetraacetate (IV) and their hydrates, can be used. These can be used alone or in combination of two or more. As a trivalent cerium ion source, inorganic cerium compounds such as cerium chloride (III), cerium oxide (III), cerium nitrate (III), cerium sulfate (III), cerium fluoride (III), cerium bromide (III), and cerium iodide (III), as well as organic cerium compounds such as cerium oxalate (III) and cerium acetate (III), and their hydrates, can be used. These cerium compounds can be used alone or in combination of two or more. As a monovalent silver ion source, inorganic silver compounds such as silver chromate (I), silver dichromate (I), silver oxide (I), potassium silver dicyanate (I), silver cyanide (I), silver bromide (I), silver nitrate (I), silver selenate (I), silver tungstate (I), silver carbonate (I), silver thiocyanate (I), silver telluride (I), silver fluoride (I), silver molybdate (I), silver iodide (I), silver sulfide (I), silver sulfate (I), silver phosphate (I), silver diphosphate (I), silver nitrite (I), silver isocyanate (I), silver chloride (I), and silver perchlorate (I), as well as organic silver compounds such as silver citrate (I), silver acetate (I), silver lactate (I), silver formate (I), and silver benzoate (I), and their hydrates, can be used. These can be used alone or in combination of two or more. The concentration of added ions in the aqueous solution is not particularly limited, as long as the content of the added element in the final cuprous oxide particles is within the preferred range mentioned above. From the viewpoint that it is easy for the added element to enter the cuprous oxide as a co-precipitate and that the co-precipitate is easy to photo-sinter, the concentration is preferably 0.001 mol to 0.1 mol relative to 1 mol of copper ions. It should be noted that by changing the concentration of added ions, the average primary particle size of the final cuprous oxide particles can be controlled.Specifically, increasing the concentration of added ions can reduce the average primary particle size of cuprous oxide particles.

[0025] As an alkaline solution, a conventional alkaline solution obtained by dissolving alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide in water can be used. Regarding the concentration of the alkali, from the viewpoint of controlling the particle size of the final cuprous oxide particles and controlling the reduction reaction, an amount of 0.1 to 10 moles of copper ions contained in the copper-containing aqueous solution mixed with the alkaline solution is preferred.

[0026] The reaction temperature for mixing an aqueous solution containing copper ions with an alkaline solution to generate copper hydroxide is not particularly limited, as long as it is between 10°C and 100°C. From the perspective of reaction control, 30°C to 95°C is preferred. It should be noted that by changing the reaction temperature, the average primary particle size of the final cuprous oxide particles can be controlled. Specifically, increasing the reaction temperature can increase the average primary particle size of the cuprous oxide particles. The reaction time is not particularly limited. Since copper hydroxide is generated immediately after mixing, depending on the concentration of copper ions, the type and concentration of the alkaline solution, and the reaction temperature, a reaction time greater than 0 minutes and less than 120 minutes is acceptable. If the reaction time exceeds 120 minutes, copper hydroxide will gradually be converted to copper oxide due to the effect of the added ions.

[0027] As reducing agents, glucose, fructose, maltose, lactose, hydroxylamine sulfate, hydroxylamine nitrate, sodium sulfite, sodium bisulfite, sodium dithionite, hydrazine, hydrazine sulfate, hydrazine phosphate, hypophosphorous acid, sodium hypophosphite, sodium borohydride, etc., can be used. Among these reducing agents, from the viewpoint of being inexpensive, readily available, easy to handle, and having high reduction efficiency for cuprous oxide, reducing sugars such as glucose and fructose are preferred. From the viewpoint of controlling the reduction reaction of copper hydroxide to cuprous oxide, the amount of reducing agent added is preferably 0.1 mol to 10 mol relative to 1 mol of copper.

[0028] The reaction temperature for reduction precipitation is not particularly limited, as long as it is between 10℃ and 100℃. From the point of view of reaction control, it is preferably between 30℃ and 95℃. The reaction time is not particularly limited, and it is usually only 5 minutes to 120 minutes.

[0029] Cuprous oxide filter cake is obtained by filtering and washing a slurry containing precipitated cuprous oxide particles. Methods for filtration and washing include: washing the slurry while the particles are fixed in a filter press; repeatedly decanting the slurry to remove the supernatant, adding pure water, stirring, and then decanting again to remove the supernatant; and repeatedly slurrying the filtered cuprous oxide particles again and filtering them again. Depending on the requirements, the obtained cuprous oxide particles can be subjected to antioxidant treatment. For example, antioxidant treatment can be performed using organic substances such as sugars, polyols, gums, heptanone, carboxylic acids, phenols, paraffin wax, and thiols, or inorganic substances such as silicon dioxide. The resulting cuprous oxide filter cake is then dried in an atmosphere and at a temperature (e.g., under vacuum, 30°C–150°C) that will not reduce it to copper or oxidize it to copper oxide. Alternatively, the obtained cuprous oxide particles can be further processed by crushing or sieving as needed.

[0030] In one embodiment of the present invention, the adhesive resin used only needs to have a carbon molar fraction of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2%. The inventors believe that by ensuring the carbon and oxygen molar fractions of the adhesive resin molecules are within the aforementioned ranges, on the one hand, not only can the cuprous oxide particles present on the surface of the coating film formed by the composition on the substrate be reduced, but also, by causing the adhesive resin present on the surface to vaporize and disappear, a highly continuous, low-resistance conductive film can be formed. On the other hand, the adhesive resin present in the lower layer of the coating film is more likely to remain, and this remaining adhesive resin improves the adhesion between the conductive film and the substrate. When the carbon molar fraction in the adhesive resin molecules is too small, the reduction of the cuprous oxide particles present on the surface of the coating film formed by the composition on the substrate is difficult to advance. Furthermore, if the light irradiation energy is increased to advance the reduction, defects such as scattering, peeling, and cracking of the conductive film may occur. On the other hand, when the carbon molar fraction in the adhesive resin molecules is too high, the light irradiation energy is consumed for carbon oxidation, leading to an increase in CO and CO2 gases, which may cause defects such as scattering, peeling, and cracking of the conductive film. Conversely, when the oxygen molar fraction in the adhesive resin molecules is too low, the CO and CO2 gases generated by the reduction of cuprous oxide particles increase, potentially causing defects such as scattering, peeling, and cracking of the conductive film. On the other hand, when the oxygen molar fraction in the adhesive resin molecules is too high, the reduction of cuprous oxide particles is difficult to advance, and if the light irradiation energy is increased to advance the reduction, defects such as scattering, peeling, and cracking of the conductive film may occur. From the viewpoint of improving adhesion while ensuring excellent conductivity, it is preferable that the carbon molar fraction in the adhesive resin molecules is 0.20% to 0.80%, and the oxygen molar fraction is 0.05% to 0.18%. It should be noted that the carbon and oxygen molar fractions in one embodiment of the present invention were measured using an elemental analysis device, the Vario EL Cube, manufactured by Elementar Corporation.

[0031] From the viewpoint that the adhesive resin used in one embodiment of the present invention is unlikely to leave excess adhesive resin in the conductive film after light irradiation, and that it can both achieve low resistance of the conductive film and easily ensure the adhesion between the substrate and the conductive film, it is preferable to have a 50% weight reduction temperature of 300°C to 500°C.

[0032] Specific examples of the aforementioned adhesive resins include cellulose resins, polyvinyl resins, unsaturated polyester resins, saturated polyester resins, terpene phenolic resins, acrylic resins, polyurea resins, polyurethane resins, polyether resins, epoxy resins, chlorinated polyolefin resins, epoxy acrylate resins, phenolic resins, melamine resins, alkyd resins, etc. These adhesive resins can be used alone or in combination of two or more. Since adhesive resins are typically used after being dissolved in an organic solvent, it is sufficient to select a resin from the aforementioned adhesive resins that satisfies the aforementioned carbon molar fraction and oxygen molar fraction and is soluble in an organic solvent. From the viewpoint of easily forming a conductive film with fewer defects and further improving the adhesion between the conductive film and the substrate, the adhesive resin is preferably selected from at least one of cellulose resins, polyvinyl resins, unsaturated polyester resins, saturated polyester resins, terpene phenolic resins, acrylic resins, polyurea resins, polyurethane resins, polyether resins, and epoxy resins.

[0033] Examples of cellulose resins include methylcellulose, ethylcellulose, propylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxypropylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose. Examples of polyethylene-based resins include polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyvinyl chloride, and polyvinylphenol. Examples of unsaturated polyester resins include polymers obtained by polymerizing unsaturated polyesters obtained from the reaction of unsaturated polyacids such as maleic acid, fumaric acid, and itaconic acid with polyols such as ethylene glycol and propylene glycol. Examples of saturated polyester resins include polyethylene terephthalate, polyethylene isophthalate, and polybutylene terephthalate. Examples of terpene phenol resins include hydrogenated terpene phenol resins. Examples of acrylic resins include poly(meth)acrylate, poly(ethyl)acrylate, and poly(meth)acrylate. Examples of polyether resins include polyethylene glycol and polypropylene glycol. Examples of epoxy resins include phenolic varnish-type epoxy resins, triphenylmethane-type epoxy resins, bisphenol A-type epoxy resins, and biphenyl-type epoxy resins. As an adhesive resin, from the viewpoint of facilitating the formation of a defect-free conductive film and further improving the adhesion between the conductive film and the substrate, at least one selected from methylcellulose, ethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, poly(meth)acrylate, poly(ethyl)acrylate, polyethylene glycol, and polypropylene glycol is preferred.

[0034] From the viewpoint that excess adhesive resin is less likely to remain in the conductive film after light exposure and that it is easier to ensure the adhesion between the substrate and the conductive film, the content of adhesive resin is preferably 0.5% to 20% by mass, more preferably 1% to 15% by mass, relative to the composition.

[0035] From the viewpoint of further improving the uniformity of the conductive film, the composition of one embodiment of the present invention may further contain a material having a uniform conductivity of 1.0 × 10⁻⁶ at 20°C. －3 Metal particles with a volume resistivity of less than Ω•cm. The preferred metal for these particles is gold (volume resistivity at 20°C: 2.4 × 10⁻⁶). －6 Ω•cm), silver (volume resistivity at 20℃: 1.6×10⁻⁶) －6 Ω•cm), copper (volume resistivity at 20℃: 1.7×10⁻⁶) －6 Ω•cm), Zinc (volume resistivity at 20℃: 5.9×10⁻⁶) －6 Ω•cm), tin (volume resistivity at 20℃: 11.4×10⁻⁶) －6 Ω•cm), aluminum (volume resistivity at 20℃: 2.75×10⁻⁶) －6 Ω•cm), nickel (volume resistivity at 20℃: 7.2×10⁻⁶) －6 Ω•cm), cobalt (volume resistivity at 20℃: 6.4×10⁻⁶) －6 (Ω•cm) and manganese (volume resistivity at 20℃: 48×10) －6 At least one of the following: (Ω•cm). From the viewpoint of good conductivity and low cost, copper particles are preferred among these metal particles. Alternatively, two or more of these metal particles can be used in combination, resulting in a product with a conductivity of 1.0 × 10⁻⁶ Ω·cm at 20°C. －3 Alloy particles with a volume resistivity below Ω•cm.

[0036] From the viewpoints of operability and photosintering, the average primary particle size of the metal particles is preferably 10 nm to 50 μm, more preferably 50 nm to 10 μm. It should be noted that, in one embodiment of the present invention, the average primary particle size of the metal particles refers to the value obtained by arbitrarily selecting 50 particles from an image observed using a scanning electron microscope (SEM), measuring the primary particle size of each particle, and then arithmetically averaging these values. Furthermore, the shape of the metal particles is not particularly limited and can be any shape among spherical, polyhedral, plate-like, irregular, agglomerated powder, or mixtures thereof.

[0037] When the composition contains the aforementioned metal particles, from the viewpoint of suppressing the increase in viscosity of the composition and forming a conductive film of sufficient thickness, the total content of cuprous oxide particles and metal particles relative to the composition is preferably 10% to 95% by mass, more preferably 20% to 85% by mass. From the viewpoint of preventing scattering during sintering, the sinterability of the conductive film, and the adhesion to the substrate, the mass ratio of metal particles to cuprous oxide particles contained in the composition of one embodiment of the present invention is preferably 95:5 to 5:95, more preferably 90:10 to 10:90.

[0038] There are no particular limitations on the organic solvent, as long as it can disperse the cuprous oxide particles and metal particles and dissolve the adhesive resin. Specific examples of organic solvents include methanol, ethanol, propanol, isopropanol, isobutanol, 1,3-propylene glycol, 1,2,3-glycerol (also known as glycerol), ethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diacetone alcohol, ethylene glycol monobutyl ether, propylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and dipropylene glycol monobutyl ether. Alcohol monopropyl ether, butyl carbitol (also known as diethylene glycol monobutyl ether), tripropylene glycol, triethylene glycol monoethyl ether, terpineol, dihydroterpineol, dihydroterpineol monoacetate, methyl ethyl ketone, cyclohexanone, ethyl lactate, propylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, dibutyl ether, octane, toluene, etc. These organic solvents can be used alone or in combination of two or more. Among these organic solvents, terpineol and butyl carbitol are preferred from the viewpoints of film drying properties, viscosity, dispersibility of cuprous oxide and metal particles, and solubility of adhesive resins.

[0039] From the viewpoints of suppressing viscosity increase of the composition, workability and photosintering properties, the content of organic solvent relative to the composition is preferably 5% to 80% by mass, more preferably 10% to 70% by mass.

[0040] The composition of one embodiment of the present invention may contain additional components other than the cuprous oxide particles, binder resin, metal particles, and solvent described above. Examples of such additional components include dispersants, protective agents, viscosity modifiers, anti-settling agents, thixotropic agents, reducing agents, affinity agents for the substrate to which the conductive film is formed, and sintering aids. However, these additional components are preferably substances that will volatilize during the drying process or be removed by vaporization during the photoreduction sintering process, and are particularly preferably compounds composed of carbon, hydrogen, oxygen, and nitrogen.

[0041] The material used as the substrate for forming the conductive film is not particularly limited, and examples include: resins such as polyethylene terephthalate, polyimide, and polyethylene naphthalate; glasses such as quartz glass, soda-lime glass, and alkali-free glass; metals such as iron, copper, and aluminum; semi-metals such as silicon and germanium; ceramics such as alumina, zirconium oxide, silicon nitride, and silicon carbide; and paper. In the conductive film forming method of one embodiment of the present invention, since the conductive film can be formed at a lower temperature in a shorter time, it is suitable for forming a conductive film on a paper substrate.

[0042] The conductive film of one embodiment of the present invention is suitable for use as wiring material, mesh electrode, heat dissipation component, etc. in IC tags, electromagnetic wave shielding bodies, electronic circuit boards, etc.

[0043] A method for forming a conductive film according to an embodiment of the present invention includes: a step of coating the above-described composition onto a substrate to form a coating film; and a step of photo-reducing and sintering cuprous oxide particles in the coating film by irradiating the coating film with light to form a conductive film, and forming an unsintered layer between the substrate and the conductive film comprising cuprous oxide particles that were not photo-reduced and remained, and adhesive resin that was not vaporized and remained.

[0044] As a method for coating the composition onto a substrate, an appropriate method can be selected based on factors such as the viscosity of the composition, the average primary particle size of the cuprous oxide particles and the metal particles. Specific coating methods include, for example, doctor blade coating, spray coating, spin coating, dip coating, roller coating, inkjet printing, gravure printing, and screen printing. The thickness of the coating film can be appropriately determined based on the thickness of the target conductive film; from the viewpoint of sintering and adhesion, a thickness of 0.1 μm to 100 μm is preferred.

[0045] In one embodiment of the conductive film formation method of the present invention, it is preferable to further include a step of drying the coating film after its formation. By removing residual organic solvents from the coating film through drying, defects in the conductive film can be reduced during the subsequent photoreduction sintering process. For drying the coating film, known dryers such as forced-air dryers or hot-air dryers can be used. The drying conditions for the coating film are typically performed at a temperature of 60°C to 120°C for 5 to 60 minutes.

[0046] To reduce and sinter cuprous oxide particles in a coating to copper, simply irradiate the coating with light using a known light irradiation device. From the viewpoint of easy temperature control, pulsed light irradiation is preferred. As pulsed light irradiation, pulsed light irradiation using a flash lamp is preferred, and pulsed light irradiation using a xenon (Xe) flash lamp is more preferred. Devices capable of performing such pulsed light irradiation include, for example, the Xenon Corporation's S-series xenon pulsed light irradiation device and the Novacentrix Pulse Forge series light sintering device. In particular, the Xenon Corporation's S-2300 can not only set voltage 1 / pulse width 1 and simple pulsed light with a single pulse, but also has the function of continuously setting voltage 2 / pulse width 2 after a single pulse, thus enabling continuous pulsed light irradiation with two or more steps under different conditions. Therefore, since the Xenon Corporation's S-2300 can adjust the irradiation energy for reduction sintering, it is suitable for the reduction sintering of cuprous oxide particles. There is no particular limit to the number of steps, as long as the cuprous oxide particles on the surface of the coating are reduced and sintered, and the cuprous oxide particles and adhesive resin in the lower layer of the coating remain. Multiple steps can also be set.

[0047] The irradiation energy and pulse width of the pulsed light are appropriately selected based on the average primary particle size of the cuprous oxide particles, the type and concentration of the binder resin, the type and concentration of the organic solvent, and the coating thickness, so as to reduce and sinter the cuprous oxide particles present on the coating surface while leaving the cuprous oxide particles and binder resin present in the lower layer of the coating. Specifically, from the viewpoint of fully reducing and sintering the cuprous oxide particles present on the coating surface, leaving the cuprous oxide particles and binder resin present in the lower layer of the coating, and reducing damage to the substrate, the cumulative pulsed light irradiation energy is preferably 0.001 J / cm². 2 ~100J / cm 2 More preferably 0.01 J / cm 2 ~30J / cm 2 From the viewpoint that cuprous oxide particles present on the surface of the coating can be fully reduced and sintered, while cuprous oxide particles and adhesive resin present in the lower layer of the coating remain, and damage to the substrate is reduced, the pulse width of the pulsed light is preferably 1 microsecond to 100 milliseconds, more preferably 10 microseconds to 10 milliseconds.

[0048] There is no particular limit to the number of pulsed light irradiations, as long as the cuprous oxide particles present on the surface of the coating are sufficiently reduced and sintered, and the cuprous oxide particles and binder resin present in the lower layer of the coating remain. The same irradiation pattern can be repeated, or various irradiation patterns can be repeated multiple times. From the viewpoint of productivity and minimizing damage to the substrate, it is preferable to reduce and sinter the coating by no more than 5 irradiations, but this is not limited to this number depending on the type of substrate.

[0049] In addition, there are no particular limitations on the atmosphere for pulsed light irradiation; it can be any atmosphere, such as atmospheric atmosphere, inert gas atmosphere, or reducing gas atmosphere.

[0050] In the method for forming the conductive film of the present invention, in order to improve the adhesion between the obtained conductive film and the substrate, it is preferable to perform a compression treatment on the conductive film formed on the substrate, and more preferably, the compression treatment is performed by applying pressure using a pressure roller. A roller press can be used for the compression treatment. The pressure conditions applied to the conductive film can be appropriately determined; from the viewpoint of achieving good adhesion with the substrate, the linear pressure is preferably 100 to 30000 kN / m.

[0051] One embodiment of the present invention includes the following technical solution.

[0052] [1] A conductive film, wherein:

[0053] The aforementioned conductive film is formed on the substrate.

[0054] The aforementioned conductive film contains a photoreduction sintered product comprising a composition including cuprous oxide particles and a binder resin.

[0055] An unsintered layer containing cuprous oxide particles that have not been photoreduced and remain, and adhesive resin is formed between the aforementioned substrate and the aforementioned conductive film.

[0056] The carbon molar fraction in the molecules of the above-mentioned adhesive resin is 0.15% to 0.9%, and the oxygen molar fraction is 0.03% to 0.2%.

[0057] [2] According to the conductive film of [1], wherein the cuprous oxide particles contain at least one additive element selected from tin, manganese, vanadium, cerium and silver.

[0058] [3] The conductive film according to [2], wherein the above-mentioned added element is tin, and its content is 150ppm to 3000ppm.

[0059] [4] The conductive film according to any one of [1] to [3], wherein the average primary particle size of the cuprous oxide particles is 1 nm to 2000 nm.

[0060] [5] The conductive film according to any one of [1] to [4], wherein the 50% weight reduction temperature of the above-mentioned adhesive resin is 300°C to 500°C.

[0061] [6] The conductive film according to any one of [1] to [5], wherein the adhesive resin comprises at least one selected from cellulose resin, polyvinyl resin, unsaturated polyester resin, saturated polyester resin, terpene phenol resin, acrylic resin, polyurea resin, polyurethane resin, polyether resin and epoxy resin.

[0062] [7] The conductive film according to any one of [1] to [6], wherein the adhesive resin comprises at least one selected from methylcellulose, ethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, poly(methyl)acrylate, poly(ethyl)acrylate, polyethylene glycol and polypropylene glycol.

[0063] [8] The conductive film according to any one of [1] to [7], wherein the composition further comprises a volume resistivity of 1.0 × 10⁻⁶ at 20°C. －3 Metal particles smaller than Ω•cm.

[0064] [9] According to the conductive film of [8], wherein the metal particles are at least one metal particle selected from gold, silver, copper, zinc, tin, aluminum, nickel, cobalt and manganese.

[0065]

[10] The conductive film according to any one of [1] to [9], wherein the substrate is paper or polyethylene terephthalate.

[0066]

[11] A method for forming a conductive film, wherein:

[0067] The above-described method is a method for forming a conductive film on a substrate, the method comprising:

[0068] The process of applying a composition comprising cuprous oxide particles and an adhesive resin onto a substrate to form a coating film; and

[0069] A conductive film is formed by photo-reducing and sintering the cuprous oxide particles in the coating film by irradiating it with light, and an unsintered layer containing unreduced cuprous oxide particles and adhesive resin is formed between the substrate and the conductive film.

[0070] The carbon molar fraction in the molecules of the above-mentioned adhesive resin is 0.15% to 0.9%, and the oxygen molar fraction is 0.03% to 0.2%.

[0071]

[12] According to the method for forming the conductive film described in

[11] , the substrate is paper or polyethylene terephthalate.

[0072]

[13] In the method for forming a conductive film according to

[11] or

[12] , the conductive film formed on the substrate is subjected to compression treatment.

[0073] Example

[0074] The present invention will be described below by way of examples, but the present invention is not limited to these examples.

[0075] <Preparation of Cuprous Oxide Particles 1>

[0076] Add 25.0 g of 48% sodium hydroxide aqueous solution and 100.0 g of pure water to a 500 mL reaction vessel. While stirring in the reaction vessel, adjust the temperature inside the reaction vessel to 40 °C to prepare an alkaline solution.

[0077] On the other hand, 17.3 g (0.1 mol) of copper(II) dihydrate, 80.0 g of pure water, and 0.45 g (0.002 mol) of tin(II) dihydrate as a divalent tin ion source were added to a 100 mL glass beaker to prepare an aqueous solution containing copper ions and divalent tin ions. While maintaining the temperature inside the reaction vessel at 40°C, the aqueous solution containing copper ions and divalent tin ions was added to the reaction vessel over approximately 2 minutes, and then stirred for 10 minutes to allow copper hydroxide to precipitate.

[0078] A reducing agent solution was prepared by adding 10.0 g of glucose and 15.0 g of pure water to a 100 mL glass beaker. After approximately 30 seconds, this reducing agent solution was added to a reaction vessel, and the temperature inside the reaction vessel was raised to 50 °C and maintained for 15 minutes. Then, stirring in the reaction vessel was stopped, and the slurry was filtered and washed to form a filter cake. The filter cake was then vacuum-dried at 80 °C for 3 hours to obtain cuprous oxide particles.

[0079] The average primary particle size of cuprous oxide particles 1 was determined based on images observed in SEM images, and was found to be 0.1 μm. Additionally, the tin content in cuprous oxide particles 1 was 570 ppm.

[0080] <Examples 1-10, Comparative Examples 1-4>

[0081] Using the cuprous oxide particles 1 obtained above, the preparation of various compositions and the formation of conductive films were carried out.

[0082] Specifically, according to the proportions shown in Table 1, cuprous oxide particles 1, binder resin, and butyl carbitol as an organic solvent were mixed in a mixer at atmospheric pressure at 1000 rpm for 30 minutes to form a paste composition. The paste composition was then screen-printed into a 1mm × 20mm rectangular pattern on a paper substrate (Mitsubishi SWORD paper, 50μm thick) to form a coating. The coating was dried at 80°C for 10 minutes under atmospheric conditions. A single pulse of light (voltage: 2700V, pulse width: 2000 microseconds) was applied to the coating formed on the paper substrate using a xenon pulsed light irradiation device (Xenon Corporation S-2300) to achieve the irradiation energy shown in Table 1, thereby forming a conductive film. Next, the conductive film and the substrate were compressed together by passing them through a roller press (60mm diameter steel rollers) at a linear pressure of 1000kN / m and a roller circumferential speed of 10mm / s. However, because the fluoropolymer used as the adhesive resin in Comparative Example 4 was insoluble in organic solvents, a coating film could not be formed.

[0083] [Table 1]

[0084]

[0085] <Preparation of Cuprous Oxide Particles 2>

[0086] Add 25.0 g of 48% sodium hydroxide aqueous solution and 100.0 g of pure water to a 500 mL reaction vessel. While stirring in the reaction vessel, adjust the temperature inside the reaction vessel to 40 °C to prepare an alkaline solution.

[0087] On the other hand, 17.3 g (0.1 mol) of copper(II) dihydrate, 80.0 g of pure water, and 0.49 g (0.002 mol) of manganese(II) acetate tetrahydrate (as a divalent manganese ion source) were added to a 100 mL glass beaker to prepare an aqueous solution containing copper ions and divalent manganese ions. While maintaining the temperature inside the reaction vessel at 40°C, the aqueous solution containing copper ions and divalent manganese ions was added to the reaction vessel over approximately 2 minutes, and then stirred for 10 minutes to allow copper hydroxide to precipitate.

[0088] A reducing agent solution was prepared by adding 10.0 g of glucose and 15.0 g of pure water to a 100 mL glass beaker. After approximately 30 seconds, this reducing agent solution was added to a reaction vessel, and the temperature inside the reaction vessel was raised to 50°C and maintained for 15 minutes. Then, stirring in the reaction vessel was stopped, and the slurry was filtered and washed to form a filter cake. The filter cake was then vacuum-dried at 80°C for 3 hours to obtain cuprous oxide particles 2.

[0089] The average primary particle size of cuprous oxide particles 2 was determined based on images observed in SEM images, and was found to be 0.1 μm. Additionally, the manganese content in cuprous oxide particles 2 was 2180 ppm.

[0090] <Examples 11-14, Comparative Examples 5-6>

[0091] Using the cuprous oxide particles 2 obtained above, various compositions were prepared and conductive films were formed.

[0092] Specifically, according to the proportions shown in Table 2, cuprous oxide particles 2, copper particles (Mitsui Metals & Mining Co., Ltd., 1100Y, average particle size 1.1 μm), binder resin, and butyl carbitol as an organic solvent were mixed in a mixer at atmospheric pressure and a speed of 1000 rpm for 30 minutes to prepare a paste composition. The paste composition was then screen-printed onto a polyethylene terephthalate substrate (Toray Industries, Ltd., Lumirror). ® A 1mm × 20mm rectangular pattern was printed on an S10 substrate (50μm thick) to form a coating. The coating was dried at 80°C for 10 minutes under atmospheric conditions. A single pulse of light (voltage: 2700V, pulse width: 2000µs) was applied to the coating on the polyethylene terephthalate substrate using a xenon pulsed light irradiation device (Xenon Corporation S-2300) to achieve the irradiation energy values ​​shown in Table 2, thereby forming a conductive film. Next, the conductive film and the substrate were compressed by passing them together between rollers (60mm diameter steel rollers) at a linear pressure of 1000kN / m and a roller circumferential speed of 10mm / s.

[0093] [Table 2]

[0094]

[0095] <Printability Evaluation>

[0096] Circuit patterns were printed on a substrate using screen printing. The printed materials were observed under a microscope, and their appearance was evaluated according to the following criteria. A circuit pattern without any defects was rated as "Excellent" printability; a circuit pattern with localized defects was rated as "Good"; and a circuit pattern with defects such as broken lines or bleeding was rated as "Unacceptable" printability. The results are shown in Table 3.

[0097] <Sinterability Evaluation>

[0098] The sintering performance was rated as "excellent" if the formed conductive film was defect-free and uniform, "good" if there were local defects or unsintered parts due to conductive film scattering, and "unacceptable" if there were defects or unsintered parts due to conductive film scattering. The results are shown in Table 3.

[0099] <Fitness Assessment>

[0100] After applying tape to the formed conductive film, the tape was peeled off. A case where no conductive film adhered to the adhesive surface of the tape and the conductive film on the paper substrate remained intact was judged as "excellent" adhesion. A case where conductive film was partially adhered to the adhesive surface of the tape, but the conductive film had no breaks, was judged as "good" adhesion. A case where conductive film adhered to the adhesive surface of the peeled tape, but the conductive film had breaks, was judged as "unacceptable". The results are shown in Table 3.

[0101] <Thickness of conductive film and unsintered layer>

[0102] The cross-section of the conductive film formed on the paper substrate was analyzed by EDS elemental mapping of copper, oxygen and carbon using scanning electron microscopy (SEM) to determine the boundary between the substrate and the unsintered layer and the boundary between the conductive film and the unsintered layer, and to determine the thickness of the conductive film and the unsintered layer. Figure 1 The images show SEM images of the cross-section of the conductive film formed on the substrate in Example 2 and EDS elemental mapping images of copper, oxygen and carbon.

[0103] [Table 3]

[0104]

[0105] As shown in Table 3, the conductive films of Examples 1-14 exhibit excellent adhesion to the substrate. On the other hand, the conductive films of Comparative Examples 1-6 show poor adhesion to the substrate.

Claims

1. A conductive film, characterized in that: The conductive film is formed on the substrate. The conductive film contains a photoreduction sintered product comprising a composition of cuprous oxide particles and a binder resin. An unsintered layer comprising cuprous oxide particles that have not been photoreduced and remain, and binder resin is formed between the substrate and the conductive film. The adhesive resin has a carbon molar fraction of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2%.

2. The conductive film according to claim 1, characterized in that: The cuprous oxide particles contain at least one additive element selected from tin, manganese, vanadium, cerium and silver.

3. The conductive film according to claim 2, characterized in that: The added element is tin, and its content is 150ppm to 3000ppm.

4. The conductive film according to claim 1 or 2, characterized in that: The average primary particle size of the cuprous oxide particles is 1 nm to 2000 nm.

5. The conductive film according to claim 1 or 2, characterized in that: The adhesive resin undergoes a 50% weight reduction at a temperature of 300°C to 500°C.

6. The conductive film according to claim 1 or 2, characterized in that: The adhesive resin comprises at least one selected from cellulose resin, polyvinyl resin, unsaturated polyester resin, saturated polyester resin, terpene phenol resin, acrylic resin, polyurea resin, polyurethane resin, polyether resin and epoxy resin.

7. The conductive film according to claim 1 or 2, characterized in that: The adhesive resin comprises at least one selected from methylcellulose, ethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, poly(methyl)acrylate, poly(ethyl)methacrylate, polyethylene glycol, and polypropylene glycol.

8. The conductive film according to claim 1 or 2, characterized in that: The composition also contains a volume resistivity of 1.0 × 10⁻⁶ at 20°C. －3 Metal particles smaller than Ω•cm.

9. The conductive film according to claim 8, characterized in that: The metal particles are selected from at least one metal particle selected from gold, silver, copper, zinc, tin, aluminum, nickel, cobalt and manganese.

10. The conductive film according to claim 1 or 2, characterized in that: The substrate is paper or polyethylene terephthalate.

11. A method for forming a conductive film, characterized in that: The forming method is a method of forming a conductive film on a substrate, the forming method comprising: The process of applying a composition comprising cuprous oxide particles and an adhesive resin onto a substrate to form a coating film; and A conductive film is formed by photo-reducing and sintering the cuprous oxide particles in the coating film by irradiating it with light, and an unsintered layer containing unreduced cuprous oxide particles and adhesive resin is formed between the substrate and the conductive film. The adhesive resin has a carbon molar fraction of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2%.

12. The method for forming a conductive film according to claim 11, characterized in that: The substrate is paper or polyethylene terephthalate.

13. The method for forming a conductive film according to claim 11 or 12, characterized in that: The conductive film formed on the substrate is compressed.

Images