Conductive film and method for forming the same

Abstract

To provide a conductive film having excellent adhesion to a base material.SOLUTION: This conductive film is formed on a base material. The conductive film is composed of a photoreduced sintered material of a composition including cuprous oxide particles and a binder resin. An unsintered layer including cuprous oxide particles remaining without being photoreduced and the binder resin is formed between the base material and the conductive film. The mole fraction of carbon in the molecule of the binder resin is 0.15% to 0.9%, and the mole fraction of oxygen is 0.03% to 0.2%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a conductive film and a method for forming the conductive film.

Background Art

[0002] With the spread of IC tags and the like, techniques for forming conductive films not only on polyethylene terephthalate (PET) films but also on paper and the like have been developed. In particular, in the case of a substrate such as paper, in order to minimize the influence of heat on the substrate, it is required to form a conductive film by heating at a low temperature for a shorter time, and moreover, it is required to have the same conductivity as when the conductive film is formed by heating at a high temperature. As a method for forming such a conductive film, for example, a photo-sintering type composition containing copper oxide particles, a solvent, and a binder resin is applied to a substrate to form a coating film, and the copper oxide particles in the coating film are reduced to copper by irradiating light to the coating film to form a conductive film (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conductive film formed by the techniques described in Patent Documents 1 and 2 has a problem that the adhesion to the substrate is insufficient.

[0005] Therefore, an object of the present invention is to provide a conductive film having excellent adhesion to a substrate and a method for forming the same.

Means for Solving the Problems

[0006] As a result of intensive studies in view of the above circumstances, the present inventors have found that the above problems can be solved by providing an un-sintered layer containing cuprous oxide particles and a specific binder resin that remain un-photoreduced between a conductive film composed of a photoreduction sintered product of a composition containing cuprous oxide particles and a specific binder resin and a substrate, and thus have completed the present invention.

[0007] That is, the present invention is a conductive film formed on a substrate, wherein the conductive film is composed of a photoreduction sintered product of a composition containing cuprous oxide particles and a binder resin, and an un-sintered layer containing cuprous oxide particles and a binder resin that remain un-photoreduced is formed between the substrate and the conductive film, and the carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%. Further, the present invention is a method for forming a conductive film on a substrate, comprising a step of applying a composition containing cuprous oxide particles and a binder resin to the substrate to form a coating film, and irradiating the coating film with light to photoreduction sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an un-sintered layer containing cuprous oxide particles and a binder resin that remain un-photoreduced between the substrate and the conductive film, and the carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a conductive film having excellent adhesion to a substrate and a method for forming the same.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] The conductive film according to an embodiment of the present invention is formed on a substrate and is composed of a photoreduced sintered product of a composition containing cuprous oxide particles and a binder resin. An unsintered layer containing cuprous oxide particles and a binder resin that remained without being photoreduced is formed between the substrate and the conductive film. The carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%. In the conductive film according to an embodiment of the present invention, by providing a predetermined unsintered layer between the substrate and the conductive film, while ensuring excellent conductivity, the binder resin in the unsintered layer exerts an adhesion effect, thereby improving the adhesion between the substrate and the conductive film. As described above, the unsintered layer contains cuprous oxide particles and a binder resin that remained without being photoreduced, but may contain a small amount of copper formed by photoreduction of some cuprous oxide particles. From the viewpoint of improving the 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, and more preferably 20:80 to 90:10. When the ratio of the conductive film is smaller than 10:90 of the ratio of the thickness of the conductive film to the thickness of the unsintered layer, it becomes difficult to obtain sufficient conductivity. When the ratio of the conductive film is larger than 98:2 of the ratio of the thickness of the conductive film to the thickness of the unsintered layer, there is a possibility that the contribution of the adhesion effect of the unsintered layer cannot be sufficiently obtained. In an embodiment of the present invention, after performing a compression treatment on the conductive film formed on the substrate, EDS elemental mapping analysis of copper, oxygen, and carbon elements is performed by a scanning electron microscope (SEM) on the cross-section, the boundary between the substrate and the unsintered layer and the boundary between the conductive film and the unsintered layer are determined, the thickest portions of the conductive film and the unsintered layer are specified from those boundaries, and they are taken as the thicknesses of the conductive film and the unsintered layer, respectively.

[0011] In one embodiment of the present invention, the cuprous oxide particles to be used are not particularly limited as long as they can be reduced to copper by light irradiation, and commercially available products may be used. Further, the method for producing the cuprous oxide particles is not particularly limited. The shape of the cuprous oxide particles is not particularly limited and may be any of spherical, polyhedral, amorphous, etc. From the viewpoint of excellent handleability and photo-sinterability, the average primary particle diameter 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. The average primary particle diameter of the cuprous oxide particles in one embodiment of the present invention is the arithmetic average of the primary particle diameters of 50 arbitrarily selected cuprous oxide particles measured in an image obtained by observing the cuprous oxide particles with a scanning electron microscope (SEM).

[0012] From the viewpoint of suppressing an increase in the viscosity of the composition and forming a conductive film having a sufficient thickness, the cuprous oxide particles are preferably contained in the composition in an amount of 3% by mass to 95% by mass, and more preferably 5% by mass to 85% by mass.

[0013] In one embodiment of the present invention, the cuprous oxide particles used are preferably contained with at least one additive element selected from the group consisting of tin, manganese, vanadium, cerium, and silver from the viewpoint of forming a conductive film with few defects and being uniform. The preferable content of the additive element varies depending on the type of the additive element, but may be within the range of 1 ppm to 30,000 ppm. When the additive element is tin, from the viewpoints of the solubility of tin ions and the control of the particle diameter of the cuprous oxide particles, 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 viewpoints of the solubility of manganese ions and the control of the particle diameter of the cuprous oxide particles, 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 the additive element is vanadium, from the viewpoints of the solubility of vanadium ions and the control of the particle diameter of the cuprous oxide particles, 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 the additive element is cerium, from the viewpoints of the solubility of cerium ions and the control of the particle diameter of the cuprous oxide particles, 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 the additive element is silver, from the viewpoints of the solubility of silver ions and the control of the particle diameter of the cuprous oxide particles, 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 additive elements, tin is preferable from the viewpoints of having a low melting point and a low resistance. In the present invention, the content of the additive element in the cuprous oxide particles is a value measured by dissolving 1 g of cuprous oxide in 10 ml of concentrated hydrochloric acid and analyzing the solution with an ICP emission spectrometer (ICPS-8100 manufactured by Shimadzu Corporation).

[0014] The cuprous oxide particles containing the above-mentioned additive elements can be produced, for example, by mixing an aqueous solution containing copper ions and at least one additive ion selected from the group consisting of divalent tin ions, divalent manganese ions, tetravalent vanadium ions, trivalent cerium ions, and monovalent silver ions with an alkaline solution to form copper hydroxide, and then adding a reducing agent to reductively precipitate the cuprous oxide particles. When forming copper hydroxide and when reductively precipitating the cuprous oxide particles, it is preferable to stir the reaction solution so that the reaction solution becomes uniform. The average primary particle diameter of the cuprous oxide particles can be adjusted by conditions such as the additive ion concentration during the production of the cuprous oxide particles and the mixing temperature of the copper ion-containing aqueous solution and the alkaline solution.

[0015] As the copper ion source contained in the aqueous solution, 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 borofluoride, copper hydroxide, and copper pyrophosphate, organic copper compounds such as copper acetate and copper lactate, and their hydrates can be used. These copper ion sources may be used alone or in combination of two or more. Among these copper ion sources, it is preferable to use copper chloride and copper sulfate from the viewpoints 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.

[0016] At least one additive ion selected from the group consisting of divalent tin ions, divalent manganese ions, trivalent and tetravalent vanadium ions, trivalent cerium ions, and monovalent silver ions contained in an aqueous solution has the effect of reducing the average primary particle diameter of the obtained cuprous oxide particles and improving the reduction sinterability to copper. As the divalent tin ion source, inorganic tin compounds such as tin(II) chloride, tin(II) sulfate, tin(II) oxide, tin(II) fluoride, tin(II) bromide, tin(II) iodide, etc., organic tin compounds such as tin(II) acetate, and their hydrates can be used. These may be used alone or in combination of two or more. As the divalent manganese ion source, inorganic manganese compounds such as manganese(II) sulfate, manganese(II) chloride, manganese(II) nitrate, etc., organic manganese compounds such as manganese(II) acetate, and their hydrates can be used. These may be used alone or in combination of two or more. As the tetravalent vanadium ion source, inorganic vanadium compounds such as vanadium(IV) oxide sulfate, vanadium(IV) tetrachloride, vanadium(IV) oxychloride, vanadium(III) chloride, vanadium(III) oxide, vanadium(IV) oxide, etc., organic vanadium compounds such as vanadium(IV) tetraacetate, and their hydrates can be used. These may be used alone or in combination of two or more. As the trivalent cerium ion source, inorganic cerium compounds such as cerium(III) chloride, cerium(III) oxide, cerium(III) nitrate, cerium(III) sulfate, cerium(III) fluoride, cerium(III) bromide, cerium(III) iodide, etc., organic cerium compounds such as cerium(III) oxalate, cerium(III) acetate, and their hydrates can be used. These may be used alone or in combination of two or more.As the monovalent silver ion source, inorganic silver compounds such as silver(I) chromate, silver(I) dichromate, silver(I) oxide, potassium dicyanoargentate(I), silver(I) cyanide, silver(I) bromide, silver(I) nitrate, silver(I) selenate, silver(I) tungstate, silver(I) carbonate, silver(I) thiocyanate, silver(I) telluride, silver(I) fluoride, silver(I) molybdate, silver(I) iodide, silver(I) sulfide, silver(I) sulfate, silver(I) phosphate, silver(I) diphosphate, silver(I) nitrite, silver(I) isocyanate, silver(I) chloride, silver(I) perchlorate, etc., organic silver compounds such as silver(I) citrate, silver(I) acetate, silver(I) lactate, silver(I) formate, silver(I) benzoate, etc., and their hydrates, etc. can be used. These may be used alone or in combination of two or more. The concentration of the added ions in the aqueous solution is not particularly limited as long as the content of the added element in the finally obtained cuprous oxide particles is within the above-mentioned preferable range. However, from the viewpoint that it is easily incorporated into cuprous oxide as a eutectic and the eutectic facilitates photosintering, it is preferably 0.001 mol to 0.1 mol with respect to 1 mol of copper ions. Note that by changing the concentration of the added ions, the average primary particle diameter of the finally obtained cuprous oxide particles can be controlled. Specifically, increasing the concentration of the added ions can decrease the average primary particle diameter of the cuprous oxide particles.

[0017] As the alkaline solution, general ones obtained by dissolving alkalis such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. in water can be used. The concentration of the alkali is preferably an amount such that it is 0.1 mol to 10 mol with respect to 1 mol of copper ions contained in the copper ion-containing aqueous solution mixed with the alkaline solution, from the viewpoints of controlling the particle diameter of the finally obtained cuprous oxide particles and controlling the reduction reaction.

[0018] When mixing an aqueous solution containing copper ions with an alkaline solution to produce copper hydroxide, the reaction temperature is not particularly limited, but it may be 10°C to 100°C, and from the perspective of reaction control, it is preferably 30°C to 95°C. By changing the reaction temperature here, the average primary particle diameter of the finally obtained cuprous oxide particles can be controlled. Specifically, by increasing the reaction temperature, the average primary particle diameter of the cuprous oxide particles can be increased. The reaction time is not particularly limited, but depending on the concentration of copper ions, the type and concentration of the alkaline solution, and the reaction temperature, since copper hydroxide is generated immediately after mixing, it may be more than 0 minutes to 120 minutes or less. If the reaction time exceeds 120 minutes, copper oxide is gradually generated from copper hydroxide by the action of the added ions.

[0019] As the reducing agent, 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, reducing sugars such as glucose and fructose are preferred from the viewpoints of being inexpensive, easily available, easy to handle, and having high reduction efficiency to cuprous oxide. The addition amount of the reducing agent is preferably an amount that is 0.1 mol to 10 mol with respect to 1 mol of copper ions from the viewpoint of controlling the reduction reaction from copper hydroxide to cuprous oxide.

[0020] The reaction temperature during reduction precipitation is not particularly limited, but it may be 10°C to 100°C, and from the viewpoint of reaction control, it is preferably 30°C to 95°C. The reaction time here is not particularly limited, but usually, it may be 5 minutes to 120 minutes.

[0021] The slurry containing the precipitated cuprous oxide particles is filtered and washed with water to obtain a cuprous oxide cake. Examples of the filtration and water washing methods include a method of washing with water while fixing the particles with a filter press or the like, a method of decanting the slurry, removing the supernatant, adding pure water, stirring, and then repeating the operation of decanting again to remove the supernatant liquid, and a method of repeating the operation of repulping the cuprous oxide particles after filtration and then filtering again. The obtained cuprous oxide particles may be subjected to an antioxidant treatment as necessary. For example, an antioxidant treatment is performed using organic substances such as saccharides, polyhydric alcohols, rubbers, hepton, carboxylic acids, phenols, paraffins, mercaptans, and inorganic substances such as silica. Then, the obtained cuprous oxide cake is dried in an atmosphere and at a temperature (for example, under vacuum, 30°C to 150°C) that does not reduce it to copper and does not oxidize it to copper oxide, whereby cuprous oxide particles can be obtained. Further, the obtained cuprous oxide particles may be subjected to treatments such as crushing and sieving as necessary.

[0022] In one embodiment of the present invention, the binder resin to be used may be one having a carbon molar fraction of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2% in the molecule. When the carbon molar fraction and the oxygen molar fraction in the molecule of the binder resin are within the above ranges, the cuprous oxide particles present on the surface layer of the coating film formed by applying the composition to the substrate are reduced, and the binder resin present on the surface layer is gasified and disappears, thereby forming a highly continuous low-resistance conductive film. On the other hand, the binder resin present in the lower layer of the coating film is likely to remain, and this remaining binder resin is considered to improve the adhesion between the conductive film and the substrate. If the carbon molar fraction in the molecule of the binder resin is too small, the reduction of the cuprous oxide particles present on the surface layer of the coating film formed by applying the composition to the substrate becomes difficult. When the irradiation energy of light is increased to promote the reduction, defects such as scattering, peeling, and cracking of the conductive film will occur. On the other hand, if the carbon molar fraction in the molecule of the binder resin is too large, the irradiation energy of light will be used for the oxidation of carbon, and CO and CO 2The amount of gas will increase, and defects such as scattering, peeling, and cracking of the conductive film will occur. Also, if the oxygen molar fraction in the molecule of the binder resin is too small, CO and CO generated along with the reduction of cuprous oxide particles 2 The amount of gas will increase, and defects such as scattering, peeling, and cracking of the conductive film will occur. On the other hand, if the oxygen molar fraction in the molecule of the binder resin is too large, the reduction of cuprous oxide particles will become difficult to proceed. When the irradiation energy of light is increased to promote the reduction, defects such as scattering, peeling, and cracking of the conductive film will occur. From the viewpoint of improving the adhesion while ensuring excellent conductivity, the carbon molar fraction in the molecule of the binder resin is preferably 0.20% to 0.80% and the oxygen molar fraction is preferably 0.05% to 0.18%. The carbon molar fraction and oxygen molar fraction in one embodiment of the present invention are values measured using an organic elemental analyzer vario EL cube manufactured by elementar.

[0023] From the viewpoint that the binder resin used in one embodiment of the present invention is less likely to leave excess binder resin on the conductive film after light irradiation, realizing a low resistance of the conductive film, and easily ensuring the adhesion between the base material and the conductive film, it preferably has a 50% weight loss temperature of 300°C to 500°C.

[0024] Specific examples of the above-mentioned binder resin include, for example, cellulose resin, polyvinyl resin, unsaturated polyester resin, saturated polyester resin, terpene phenol resin, acrylic resin, polyurea resin, polyurethane resin, polyether resin, epoxy resin, chlorinated polyolefin resin, epoxy acrylate resin, phenol resin, melamine resin, alkyd resin, etc. These binder resins may be used alone or in combination of two or more. Since the binder resin is usually used by dissolving it in an organic solvent, it may be selected from the above-mentioned binder resins that satisfy the above-mentioned carbon molar fraction and oxygen molar fraction and are soluble in the organic solvent. From the viewpoint of easily forming a defect-free conductive film and further improving the adhesion between the conductive film and the substrate, the binder resin is preferably at least one selected from the group consisting of cellulose resin, polyvinyl resin, unsaturated polyester resin, saturated polyester resin, terpene phenol resin, acrylic resin, polyurea resin, polyurethane resin, polyether resin, and epoxy resin.

[0025] Examples of the cellulose resin include methyl cellulose, ethyl cellulose, propyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like. Examples of the polyvinyl resin include polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyvinyl chloride, polyvinyl phenol, and the like. Examples of the unsaturated polyester resin include those obtained by polymerizing an unsaturated polyester obtained by the reaction of an unsaturated polybasic acid such as maleic acid, fumaric acid, itaconic acid, and a polyhydric alcohol such as ethylene glycol, propylene glycol. Examples of the saturated polyester resin include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, and the like. Examples of the terpene phenol resin include hydrogenated terpene phenol resin, and the like. Examples of the acrylic resin include poly(meth)acrylic acid methyl, poly(meth)acrylic acid ethyl, poly(meth)acrylic acid propyl, and the like. Examples of the polyether resin include polyethylene glycol, polypropylene glycol, and the like. Examples of the epoxy resin include phenol novolac type epoxy resin, triphenylmethane type epoxy resin, bisphenol A type epoxy resin, biphenyl type epoxy resin, and the like. From the viewpoint of easily forming a conductive film without defects and further improving the adhesion between the conductive film and the substrate, the binder resin is preferably at least one selected from the group consisting of methyl cellulose, ethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, poly(meth)acrylic acid methyl, poly(meth)acrylic acid ethyl, polyethylene glycol, and polypropylene glycol.

[0026] From the viewpoint of being less likely to leave an excess binder resin on the conductive film after light irradiation and easily ensuring the adhesion between the substrate and the conductive film, the content of the binder resin is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, based on the composition.

[0027] From the viewpoint of further improving the uniformity of the conductive film, the composition in one embodiment of the present invention may further contain metal particles having a volume resistivity of 1.0×10 -3 Ω·cm or less at 20°C. The metal species of such metal particles is gold (volume resistivity at 20°C: 2.4×10 -6 Ω·cm), silver (volume resistivity at 20°C: 1.6×10 -6 Ω·cm), copper (volume resistivity at 20°C: 1.7×10 -6 Ω·cm), zinc (volume resistivity at 20°C: 5.9×10 -6 Ω·cm), tin (volume resistivity at 20°C: 11.4×10 -6 Ω·cm), aluminum (volume resistivity at 20°C: 2.75×10 -6 Ω·cm), nickel (volume resistivity at 20°C: 7.2×10 -6 Ω·cm), cobalt (volume resistivity at 20°C: 6.4×10 -6 Ω·cm) and manganese (volume resistivity at 20°C: 48×10 -6 Ω·cm), and is preferably at least one selected from the group consisting of these. Among these metal particles, copper particles are preferred from the viewpoints of good conductivity and low cost. Also, two or more of these metal particles may be used in combination, or alloy particles having a volume resistivity of 1.0×10 -3 Ω·cm or less at 20°C may be used.

[0028] The average primary particle diameter of the metal particles is preferably 10 nm to 50 μm, more preferably 50 nm to 10 μm, from the viewpoints of handleability and photo-sinterability. The average primary particle diameter of the metal particles in one embodiment of the present invention is the arithmetic mean of the primary particle diameters of 50 arbitrarily selected particles measured in an image observed with a scanning electron microscope (SEM). Also, the shape of the metal particles is not particularly limited and may be any of spherical, polyhedral, flake-like, amorphous, agglomerated powder, or a mixture thereof.

[0029] When the composition contains the above-described metal particles, from the viewpoint of suppressing an increase in the viscosity of the composition and forming a conductive film having a sufficient thickness, it is preferable that the total of the copper oxide particles and the metal particles be contained in the composition in an amount of 10% to 95% by mass, and more preferably 20% to 85% by mass. From the viewpoints of preventing scattering during sintering, sinterability of the conductive film, and adhesion to the substrate, the mass ratio of the metal particles to the copper oxide particles contained in the composition according to one embodiment of the present invention is preferably 95:5 to 5:95, and more preferably 90:10 to 10:90.

[0030] The organic solvent is not limited as long as it can disperse copper oxide particles and metal particles and dissolve the binder resin. Specific examples of the organic solvent include methanol, ethanol, propanol, isopropyl alcohol, isobutanol, 1,3-propanediol, 1,2,3-propanetriol (alias: glycerin), 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, dipropylene glycol monopropyl ether, butyl carbitol (alias: diethylene glycol monobutyl ether), tripropylene glycol, triethylene glycol monoethyl ether, terpineol, dihydroterpineol, dihydroterpinyl 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, and the like. These organic solvents may be used alone or in combination of two or more. Among these organic solvents, terpineol and butyl carbitol are preferable from the viewpoints of the drying property, viscosity, dispersibility of copper oxide particles and metal particles, solubility of the binder resin, and the like of the coating film.

[0031] From the viewpoints of suppressing the increase in the viscosity of the composition, handleability, and photo-sinterability, the organic solvent is preferably contained in the composition in an amount of 5% by mass to 80% by mass, more preferably 10% by mass to 70% by mass.

[0032] The composition according to an embodiment of the present invention may contain additional components other than the above-described cuprous oxide particles, binder resin, metal particles, and solvent. Such additional components include, for example, dispersants, protective agents, viscosity modifiers, anti-settling agents, thixotropic agents, reducing agents, affinity agents for the substrate to be formed with the conductive film, sintering aids, and the like. However, these additional components are preferably substances that volatilize in the drying process or are gasified and removed in the photoreduction sintering process, and more preferably compounds composed of carbon, hydrogen, oxygen, and nitrogen.

[0033] The material of the substrate to be formed with the conductive film is not particularly limited, and examples thereof include resins such as polyethylene terephthalate, polyimide, and polyethylene naphthalate; glasses such as quartz glass, soda glass, and alkali-free glass; metals such as iron, copper, and aluminum; semimetals such as silicon and germanium; ceramics such as alumina, zirconia, silicon nitride, and silicon carbide; paper, and the like. In the method for forming a conductive film according to an embodiment of the present invention, since the conductive film can be formed by low-temperature heating for a shorter time, it is suitable for forming a conductive film on a paper substrate.

[0034] The conductive film according to an embodiment of the present invention is suitable for applications such as IC tags, electromagnetic shields, wiring materials such as electronic circuit boards, mesh electrodes, and heat dissipation materials.

[0035] The method for forming a conductive film according to an embodiment of the present invention includes a step of applying the above-described composition to a substrate to form a coating film, and irradiating the coating film with light to photoreduction-sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an unsintered layer containing cuprous oxide particles that remain without being photoreduced and binder resin that remains without being gasified between the substrate and the conductive film.

[0036] As a method for applying the composition to the substrate, an appropriate method may be selected according to the viscosity of the composition, the average primary particle diameter of the cuprous oxide particles and the metal particles, etc. Specific coating methods include, for example, bar coating method, spray coating method, spin coating method, dip coating method, roll coating method, inkjet printing method, gravure printing method, screen printing method, etc. The thickness of the coating film may be appropriately determined according to the thickness of the target conductive film, but from the viewpoints of sinterability and adhesion, it is preferably 0.1 μm to 100 μm.

[0037] The method for forming a conductive film according to an embodiment of the present invention preferably further includes a step of drying the coating film after the formation of the coating film. By removing the organic solvent remaining in the coating film by drying, it is possible to reduce the occurrence of defects in the conductive film in the photoreduction firing step described later. For drying the coating film, known dryers such as a blower dryer and a hot air dryer can be used. The drying conditions of the coating film are usually 60°C to 120°C for 5 minutes to 60 minutes.

[0038] To reduce and sinter copper oxide particles in the coating film to copper, light may be irradiated onto the coating film using a known light irradiation device. From the viewpoint of facilitating temperature control, pulse light irradiation is preferably used for the light irradiation. As the pulse light irradiation, pulse light irradiation using a flash lamp is preferable, and pulse light irradiation using a xenon (Xe) flash lamp is more preferable. Examples of devices capable of performing such pulse light irradiation include the xenon pulse light irradiation device S-series manufactured by Xenon Corporation and the light firing device Pulse Forge series manufactured by Novacentrix. In particular, the S-2300 manufactured by Xenon Corporation can set a simple pulse light with voltage 1 / pulse width 1 with a single pulse light, and further has a function of setting voltage 2 / pulse width 2 continuously after voltage 1 / pulse width 1 with a single pulse light. Therefore, continuous pulse light irradiation of two or more steps with different conditions is possible. Thus, the S-2300 manufactured by Xenon Corporation is suitable for the reduction sintering of copper oxide particles because it can adjust the irradiation energy for reduction sintering. The number of steps is not particularly limited as long as the copper oxide particles present in the surface layer of the coating film can be reduced and sintered and the copper oxide particles and the binder resin present in the lower layer of the coating film can be left, and a plurality of steps may be set.

[0039] The irradiation energy and pulse width of the pulse light can be appropriately selected according to the average primary particle diameter of the copper oxide particles, the type and concentration of the binder resin, the type and concentration of the organic solvent, the thickness of the coating film, etc., so that the copper oxide particles present in the surface layer of the coating film can be reduced and sintered and the copper oxide particles and the binder resin present in the lower layer of the coating film can be left. Specifically, from the viewpoint of sufficiently reducing and sintering the copper oxide particles present in the surface layer of the coating film, leaving the copper oxide particles and the binder resin present in the lower layer of the coating film, and reducing the damage to the substrate, the cumulative pulse light irradiation energy is 0.001 J / cm 2 ~100 J / cm 2 is preferably, 0.01 J / cm 2 ~30 J / cm 2It is more preferable that it is. From the viewpoint of sufficiently reducing and sintering the copper oxide particles present in the surface layer of the coating film, leaving the copper oxide particles and the binder resin present in the lower layer of the coating film, and reducing damage to the substrate, the pulse width of the pulsed light is preferably from 1 μs to 100 ms, and more preferably from 10 μs to 10 ms.

[0040] The number of irradiations of the pulsed light is not particularly limited as long as the copper oxide particles present in the surface layer of the coating film can be sufficiently reduced and sintered and the copper oxide particles and the binder resin present in the lower layer of the coating film can be left. The same irradiation pattern may be repeated, or various irradiation patterns may be repeated several times. From the viewpoints of productivity and damage to the substrate, it is preferable to perform reduction sintering by irradiation within 5 times, but this is not the case depending on the type of the substrate.

[0041] Also, the atmosphere for performing the pulsed light irradiation is not particularly limited, and it may be any of an air atmosphere, an inert gas atmosphere, a reducing gas atmosphere, and the like.

[0042] In the method for forming the conductive film of the present invention, in order to enhance the adhesion between the obtained conductive film and the substrate, it is preferable to compress the conductive film formed on the substrate, and it is more preferable that this compression treatment is performed by pressurizing with a roll. A roll press machine can be used for the compression treatment. The pressurization conditions for the conductive film may be appropriately determined, but from the viewpoint of improving the adhesion to the substrate, the line pressure is preferably 100 to 30000 kN / m.

[0043] One embodiment of the present invention includes the following. [1] A conductive film formed on a substrate, The conductive film is composed of a photoreduced sintered product of a composition containing copper oxide particles and a binder resin, An unsintered layer containing copper oxide particles and a binder resin that remained without being photoreduced is formed between the substrate and the conductive film, A conductive film in which the carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%. [2] The conductive film according to [1], wherein the cuprous oxide particles contain at least one additive element selected from the group consisting of tin, manganese, vanadium, cerium, and silver. [3] The conductive film according to [2], wherein the additive element is tin and the content thereof is 150 ppm to 3000 ppm. [4] The conductive film according to any one of [1] to [3], wherein the average primary particle diameter of the cuprous oxide particles is 1 nm to 2000 nm. [5] The conductive film according to any one of [1] to [4], wherein the 50% weight loss temperature of the binder resin is 300°C to 500°C. [6] The conductive film according to any one of [1] to [5], wherein the binder resin contains at least one selected from the group consisting of 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 any one of [1] to [6], wherein the binder resin contains at least one selected from the group consisting of methyl cellulose, ethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, poly(meth)acrylate methyl, poly(meth)acrylate ethyl, polyethylene glycol, and polypropylene glycol. [8] The composition further contains metal particles having a volume resistivity at 20°C of 1.0×10 -3 Ω·cm or less, and the conductive film according to any one of [1] to [7]. [9] The conductive film according to [8], wherein the metal particles are at least one kind of metal particles selected from the group consisting of gold, silver, copper, zinc, tin, aluminum, nickel, cobalt, and manganese.

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

[11] A method for forming a conductive film on a substrate, A step of applying a composition containing cuprous oxide particles and a binder resin to a substrate to form a coating film By irradiating the coating film with light, while photo-reducing and sintering the cuprous oxide particles in the coating film to form a conductive film, an unsintered layer containing cuprous oxide particles and a binder resin that remained without being photo-reduced is formed between the substrate and the conductive film Comprising A method for forming a conductive film, wherein the carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar ratio is 0.03% to 0.2%

[12] The method for forming a conductive film according to

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

[13] The method for forming a conductive film according to

[11] or

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

Example

[0044] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples

[0045] <Preparation of cuprous oxide particles 1> 25.0 g of a 48% by mass aqueous sodium hydroxide solution and 100.0 g of pure water were added to a 500 mL reaction vessel, and while stirring the inside of the reaction vessel, the temperature inside the reaction vessel was adjusted to 40 °C to prepare an alkaline solution On the other hand, 17.3 g (0.1 mol) of copper(II) chloride dihydrate, 80.0 g of pure water, and 0.45 g (0.002 mol) of tin(II) chloride 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 about 2 minutes, and then stirred for 10 minutes to precipitate copper hydroxide

[0046] 10.0 g of glucose and 15.0 g of pure water were added to a 100 mL glass beaker to prepare a reducing agent solution. After adding this reducing agent solution to the reaction vessel over about 30 seconds, the temperature inside the reaction vessel was raised to 50 °C and maintained for 15 minutes. Then, the stirring inside the reaction vessel was stopped, and the slurry was filtered and washed to prepare a cake. This cake was vacuum dried at 80 °C for 3 hours to obtain copper oxide particles 1.

[0047] The average primary particle size of the copper oxide particles 1 was determined to be 0.1 μm from the image observed in the electron micrograph (SEM) of the obtained copper oxide particles 1. Also, the tin content contained in the copper oxide particles 1 was 570 ppm.

[0048] <Examples 1 to 10, Comparative Examples 1 to 4> Using the copper oxide particles 1 obtained above, each composition was prepared and a conductive film was formed. Specifically, at the blending ratios shown in Table 1, copper oxide particles 1, a binder resin, and butyl carbitol as an organic solvent were kneaded at 1000 rpm for 30 minutes under atmospheric pressure using a kneader to prepare a paste-like composition. The paste-like composition was screen-printed onto a paper substrate (SWORD manufactured by Mitsubishi Paper Mills, thickness 50 μm) to print a 1 mm × 20 mm rectangular pattern to form a coating film. The coating film was dried at 80 °C for 10 minutes in an air atmosphere. A conductive film was formed by irradiating the coating film formed on the paper substrate with 1 pulse of pulsed light (voltage: 2700 V, pulse width: 2000 microseconds) using a xenon pulsed light irradiation device (S-2300 manufactured by Xenon Corporation) so that the pulsed light irradiation energy became the value shown in Table 1. Next, the conductive film together with the substrate was passed between the rolls of a roll press machine (steel roll with a diameter of 60 mm) and pressurized by passing at a linear pressure of 1000 kN / m and a peripheral speed of the roll of 10 mm / s to perform a compression treatment. However, in Comparative Example 4, since the fluororesin used as the binder resin did not dissolve in the organic solvent, a coating film could not be formed.

[0049]

Table 1

[0050] <Production of Cuprous Oxide Particles 2> 25.0 g of a 48 mass% aqueous sodium hydroxide solution and 100.0 g of pure water were added to a 500 mL reaction vessel, and while stirring the inside of the reaction vessel, the temperature inside the reaction vessel was adjusted to 40 °C to prepare an alkaline solution. On the other hand, 17.3 g (0.1 mol) of copper(II) chloride 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 about 2 minutes, and then stirred for 10 minutes to precipitate copper hydroxide.

[0051] 10.0 g of glucose and 15.0 g of pure water were added to a 100 mL glass beaker to prepare a reducing agent solution. This reducing agent solution was added to the reaction vessel over about 30 seconds, and then the temperature inside the reaction vessel was raised to 50 °C and held for 15 minutes. Thereafter, stirring inside the reaction vessel was stopped, and the slurry was filtered and washed to prepare a cake. This cake was vacuum dried at 80 °C for 3 hours to obtain cuprous oxide particles 2.

[0052] The average primary particle diameter of the obtained cuprous oxide particles 2 was determined to be 0.1 μm from the image observed by an electron micrograph (SEM) of the cuprous oxide particles 2. Also, the manganese content contained in the cuprous oxide particles 2 was 2180 ppm.

[0053] <Examples 11 to 14, Comparative Examples 5 to 6> Using the cuprous oxide particles 2 obtained above, each composition was prepared and a conductive film was formed. Specifically, cuprous oxide particles 2, copper particles (manufactured by Mitsui Mining & Smelting Co., Ltd., 1100Y, average particle diameter 1.1 μm), a binder resin, and butyl carbitol as an organic solvent were kneaded at 1,000 rpm for 30 minutes under atmospheric pressure using a kneader to prepare a paste-like composition. The paste-like composition was screen-printed onto a polyethylene terephthalate substrate (manufactured by Toray Industries, Inc., Lumirror S10, thickness 50 μm) to form a coating film by printing a rectangular pattern of 1 mm × 20 mm. The coating film was dried at 80°C for 10 minutes in an air atmosphere. A pulse light was irradiated once (voltage: 2700 V, pulse width: 2000 microseconds) onto the coating film formed on the polyethylene terephthalate substrate using a xenon pulse light irradiation device (S-2300 manufactured by Xenon Corporation) so that the pulse light irradiation energy became the value shown in Table 2, thereby forming a conductive film. Next, the conductive film together with the substrate was passed between the rolls of a roll press machine (steel roll with a diameter of 60 mm) and pressurized at a linear pressure of 1000 kN / m and a peripheral speed of the roll of 10 mm / s to perform a compression treatment.

[0054]

Table 2

[0055] <Printability evaluation> A wiring pattern was printed on the substrate by the screen printing method, the printed matter was observed under a microscope, and the appearance was evaluated according to the following criteria. Those with no defects in all wiring patterns were judged as having "excellent" printability, those with some defects in the wiring patterns were judged as having "good" printability, and those with disconnection or bleeding in the wiring patterns were judged as having "unacceptable" printability. The results are shown in Table 3.

[0056] <Sinterability evaluation> Those with no defects and being uniform in the formed conductive film were judged as having "excellent" sinterability, those with some defects due to the scattering of the conductive film or those with some un-sintered parts were judged as having "good" sinterability, and those with defects or un-sintered due to the scattering of the conductive film were judged as having "unacceptable" sinterability. The results are shown in Table 3.

[0057] <Adhesion Evaluation> After attaching a tape to the formed conductive film, the tape was peeled off. Those in which the conductive film was not attached to the adhesive surface of the tape and the conductive film formed on the paper substrate remained intact were judged to have "excellent" adhesion. Those in which the conductive film was attached to a part of the adhesive surface of the tape but there was no disconnection in the conductive film were judged to have "good" adhesion. Those in which the conductive film was attached to the adhesive surface of the peeled tape and the conductive film was disconnected were judged to have "unacceptable" adhesion. The results are shown in Table 3.

[0058] <Thickness of Conductive Film and Unsintered Layer> Cross-sectional analysis of the conductive film formed on the paper substrate was performed by EDS elemental mapping analysis of copper, oxygen, and carbon elements using a scanning electron microscope (SEM). The boundaries between the substrate and the unsintered layer and between the conductive film and the unsintered layer were determined, and the thicknesses of the conductive film and the unsintered layer were obtained. Figure 1 shows the SEM image and the EDS elemental mapping images of copper, oxygen, and carbon elements for the cross-section of the conductive film formed on the substrate in Example 2.

[0059]

Table 3

[0060] As can be seen from the results in Table 3, the conductive films of Examples 1 to 14 had excellent adhesion to the substrate. On the other hand, the conductive films of Comparative Examples 1 to 6 had low adhesion to the substrate.

Claims

1. A conductive film formed on a substrate, the conductive film is made of a photoreduced sintered product of a composition containing cuprous oxide particles and a binder resin; an unsintered layer is formed between the substrate and the conductive film, the unsintered layer including cuprous oxide particles and a binder resin that have not been photoreduced, The conductive film, wherein the carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%.

2. The conductive film according to claim 1 , wherein the cuprous oxide particles contain at least one additive element selected from the group consisting of tin, manganese, vanadium, cerium, and silver.

3. 3. The conductive film according to claim 2, wherein the added element is tin and the content thereof is 150 ppm to 3000 ppm.

4. The conductive film according to claim 1 or 2, wherein the cuprous oxide particles have an average primary particle diameter of 1 nm to 2000 nm.

5. 3. The conductive film according to claim 1, wherein the binder resin has a 50% weight loss temperature of 300° C. to 500° C.

6. 3. The conductive film according to claim 1, wherein the binder resin comprises at least one selected from the group consisting of a cellulose resin, a polyvinyl resin, an unsaturated polyester resin, a saturated polyester resin, a terpene phenol resin, an acrylic resin, a polyurea resin, a polyurethane resin, a polyether resin, and an epoxy resin.

7. 3. The conductive film according to claim 1, wherein the binder resin comprises at least one selected from the group consisting of methyl cellulose, ethyl cellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polyethylene glycol, and polypropylene glycol.

8. The composition has a volume resistivity of 1.0×10 －３ The conductive film according to claim 1 or 2, further comprising metal particles having a resistivity of Ω·cm or less.

9. 9. The conductive film according to claim 8, wherein the metal particles are at least one type of metal particles selected from the group consisting of gold, silver, copper, zinc, tin, aluminum, nickel, cobalt, and manganese.

10. The conductive film according to claim 1 or 2, wherein the substrate is paper or polyethylene terephthalate.

11. A method for forming a conductive film on a substrate, comprising the steps of: A step of applying a composition containing cuprous oxide particles and a binder resin to a substrate to form a coating film; a step of irradiating the coating film with light to photo-reduce and sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an unsintered layer between the base material and the conductive film, the unsintered layer including the cuprous oxide particles and the binder resin that have not been photo-reduced and remain; Equipped with The method for forming a conductive film, wherein the carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%.

12. The method for forming a conductive film according to claim 11 , wherein the substrate is paper or polyethylene terephthalate.

13. The method for forming a conductive film according to claim 11 or 12, further comprising the step of compressing the conductive film formed on the substrate.

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