Conductive film and method for forming same

Abstract

Provided is a conductive film having excellent adhesion to a base material. 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 which includes the binder resin and the cuprous oxide particles having not been photoreduced is formed between the base material and the conductive film. The carbon mole fraction and the oxygen mole fraction per molecule of the binder resin are 0.15-0.9% and 0.03-0.2%, respectively.

Description

Conductive film and method for forming same

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

[0002] With the widespread use of IC tags and the like, technologies 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 substrates such as paper, it is necessary to form a conductive film by low-temperature heating for a shorter period of time in order to minimize the thermal effects on the substrate, and yet to have conductivity equivalent to that of a conductive film formed by high-temperature heating. As a method for forming such a conductive film, for example, a technology is known in which a photosintering composition containing cuprous oxide particles, a solvent, and a binder resin is applied to a substrate to form a coating film, and the coating film is then irradiated with light to reduce the cuprous oxide particles in the coating film to copper, thereby forming a conductive film (see Patent Documents 1 and 2).

[0003] JP 2019-149360 A JP 2019-200912 A

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

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

[0006] As a result of extensive research conducted in light of the above-mentioned circumstances, the present inventors discovered that the above-mentioned problems can be solved by providing an unsintered layer containing cuprous oxide particles and a specific binder resin that remain without being photoreduced between a substrate and a conductive film made of a photoreduced sintered product of a composition containing cuprous oxide particles and a specific binder resin, and thus completed the present invention.

[0007] That is, the present invention provides a conductive film formed on a substrate, the conductive film comprising a photoreduced and sintered product of a composition containing cuprous oxide particles and a binder resin, wherein an unsintered layer containing the cuprous oxide particles and binder resin that remain unphotoreduced is formed between the substrate and the conductive film, and the carbon molar fraction in the binder resin molecule is 0.15% to 0.9% and the oxygen molar fraction in the binder resin molecule is 0.03% to 0.2%. The present invention also provides a method for forming a conductive film on a substrate, the method comprising the steps 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 photoreducibly sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an unsintered layer containing the cuprous oxide particles and binder resin that remain unphotoreduced between the substrate and the conductive film, wherein the carbon molar fraction in the binder resin molecule is 0.15% to 0.9% and the oxygen molar fraction in the binder resin molecule is 0.03% to 0.2%.

[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.

[0009] 1 shows an SEM image of a cross section of a conductive film formed on a substrate in Example 2, and EDS element mapping images of copper, oxygen, and carbon elements.

[0010] A conductive film according to one embodiment of the present invention is formed on a substrate and comprises a photoreduced sintered product of a composition containing cuprous oxide particles and a binder resin. Between the substrate and the conductive film, an unsintered layer is formed containing cuprous oxide particles and binder resin that remain unphotoreduced. The carbon molar fraction in the binder resin molecule is 0.15% to 0.9% and the oxygen molar fraction is 0.03% to 0.2%. In the conductive film according to one embodiment of the present invention, the provision of a predetermined unsintered layer between the substrate and the conductive film ensures excellent conductivity, while the binder resin in the unsintered layer exerts an adhesive effect, improving adhesion between the substrate and the conductive film. As described above, the unsintered layer contains cuprous oxide particles and binder resin that remain unphotoreduced. However, some of the cuprous oxide particles may contain a small amount of copper resulting from photoreducing. From the viewpoint of improving adhesion to various substrates while ensuring excellent conductivity, the ratio of the thickness of the conductive film to the thickness of the unsintered layer after compression treatment is preferably 10:90 to 98:2, and more preferably 20:80 to 90:10. When the ratio of the conductive film thickness to the unsintered layer thickness is smaller than 10:90, it becomes difficult to obtain sufficient conductivity, and when the ratio of the conductive film thickness to the unsintered layer thickness is greater than 98:2, it may become difficult to obtain the sufficient adhesive effect of the unsintered layer. In one embodiment of the present invention, a cross section of a conductive film formed on a substrate after compression treatment is subjected to EDS elemental mapping analysis of copper, oxygen, and carbon elements 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, and the thickest points of the conductive film and the unsintered layer are identified from these boundaries, and these are taken as the thicknesses of the conductive film and the unsintered layer, respectively.

[0011] The cuprous oxide particles used in one embodiment of the present invention are not particularly limited as long as they are reduced to copper by irradiation with light, and commercially available products may be used. Furthermore, the method for producing the cuprous oxide particles is not particularly limited. The shape of the cuprous oxide particles is not particularly limited, and they may be spherical, polyhedral, irregular, or the like. From the viewpoint of excellent handleability and photosinterability, 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 determined by measuring the primary particle diameter of 50 randomly selected cuprous oxide particles in an image of the cuprous oxide particles observed with a scanning electron microscope (SEM), and then arithmetically averaging these values.

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

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

[0014] The cuprous oxide particles containing the above-described additive element 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 generate copper hydroxide, and then adding a reducing agent to reduce and precipitate the cuprous oxide particles. When generating copper hydroxide and when reducing and precipitating the cuprous oxide particles, it is preferable to stir the reaction solution so that it becomes homogeneous. The average primary particle size of the cuprous oxide particles can be adjusted by conditions such as the concentration of the additive ions during the production of the cuprous oxide particles and the mixing temperature of the copper ion-containing aqueous solution and the alkaline solution.

[0015] Examples of copper ion sources that can be contained in the aqueous solution include 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 fluoroborate, copper hydroxide, and copper pyrophosphate, and organic copper compounds such as copper acetate and copper lactate, as well as hydrates thereof. These copper ion sources may be used alone or in combination. Among these copper ion sources, copper chloride and copper sulfate are preferred because of their 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] The addition of at least one added 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 in the aqueous solution reduces the average primary particle size of the resulting cuprous oxide particles and improves the reductive sinterability to copper. Examples of divalent tin ion sources include inorganic tin compounds such as tin(II) chloride, tin(II) sulfate, tin(II) oxide, tin(II) fluoride, tin(II) bromide, and tin(II) iodide, organic tin compounds such as tin(II) acetate, and hydrates thereof. These may be used alone or in combination of two or more. Examples of divalent manganese ion sources include inorganic manganese compounds such as manganese(II) sulfate, manganese(II) chloride, and manganese(II) nitrate, organic manganese compounds such as manganese(II) acetate, and hydrates thereof. These may be used alone or in combination of two or more. Examples of tetravalent vanadium ion sources that can be used include inorganic vanadium compounds such as vanadium(IV) oxide sulfate, vanadium(IV) tetrachloride, vanadium(IV) oxide hydrochloride, vanadium(III) chloride, vanadium(III) oxide, and vanadium(IV) oxide; organic vanadium compounds such as vanadium(IV) tetraacetate; and hydrates thereof. These may be used alone or in combination of two or more. Examples of trivalent cerium ion sources that can be used include inorganic cerium compounds such as cerium(III) chloride, cerium(III) oxide, cerium(III) nitrate, cerium(III) sulfate, cerium(III) fluoride, cerium(III) bromide, and cerium(III) iodide; organic cerium compounds such as cerium(III) oxalate and cerium(III) acetate; and hydrates thereof. These may be used alone or in combination of two or more.As the monovalent silver ion source, inorganic silver compounds such as silver chromate (I), silver dichromate (I), silver oxide (I), potassium dicyanoargentate (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), 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 may 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 elements in the cuprous oxide particles finally obtained falls within the above-mentioned preferred range, but from the viewpoint of being easily incorporated into the cuprous oxide as a co-deposit and facilitating photosintering of the co-deposit, it is preferable that the concentration be 0.001 mol to 0.1 mol per mol of copper ions. Note that by changing the concentration of added ions, the average primary particle size of the cuprous oxide particles finally obtained can be controlled. Specifically, increasing the concentration of added ions can reduce the average primary particle size of the cuprous oxide particles.

[0017] As the alkaline solution, a common solution in which an alkali such as sodium hydroxide, potassium hydroxide, or lithium hydroxide is dissolved in water can be used. From the viewpoint of controlling the particle size of the cuprous oxide particles finally obtained and controlling the reduction reaction, the concentration of the alkali is preferably an amount of 0.1 mol to 10 mol per 1 mol of copper ions contained in the copper ion-containing aqueous solution to be mixed with the alkaline solution.

[0018] The reaction temperature when mixing the copper ion-containing aqueous solution with the alkaline solution to produce copper hydroxide is not particularly limited, but may be 10°C to 100°C, and from the viewpoint of reaction control, is preferably 30°C to 95°C. The average primary particle size of the cuprous oxide particles finally obtained can be controlled by changing the reaction temperature. Specifically, the average primary particle size of the cuprous oxide particles can be increased by increasing the reaction temperature. The reaction time is not particularly limited, but may be longer than 0 minutes and shorter than 120 minutes, since copper hydroxide may be produced immediately after mixing depending on the copper ion concentration, the type and concentration of the alkaline solution, and the reaction temperature. If the reaction time exceeds 120 minutes, copper oxide is gradually produced from the copper hydroxide due to the action of the added ions.

[0019] Examples of reducing agents that can be used include glucose, fructose, maltose, lactose, hydroxylamine sulfate, hydroxylamine nitrate, sodium sulfite, sodium bisulfite, sodium dithionite, hydrazine, hydrazine sulfate, hydrazine phosphate, hypophosphorous acid, sodium hypophosphite, and sodium borohydride. Among these reducing agents, reducing sugars such as glucose and fructose are preferred from the viewpoints of being inexpensive, readily available, easy to handle, and having a high efficiency of reduction to cuprous oxide. The amount of reducing agent added is preferably 0.1 to 10 moles per mole of copper ions from the viewpoint of controlling the reduction reaction from copper hydroxide to cuprous oxide.

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

[0021] A cuprous oxide cake is obtained by filtering the slurry containing the precipitated cuprous oxide particles and washing with water. Examples of filtration and washing methods include washing the particles while they are immobilized using a filter press or the like; decanting the slurry, removing the supernatant, adding pure water, stirring, and then decanting again to remove the supernatant, repeating this process; and repulping the filtered cuprous oxide particles and then filtering again, repeating this process. The obtained cuprous oxide particles may be subjected to an antioxidant treatment, if necessary. For example, an antioxidant treatment may be performed using organic substances such as sugars, polyhydric alcohols, rubber, heptone, carboxylic acids, phenols, paraffin, and mercaptans, or inorganic substances such as silica. The obtained cuprous oxide cake can then be dried in an atmosphere and at a temperature (e.g., under vacuum, 30°C to 150°C) that neither reduces the cuprous oxide to copper nor oxidizes it to copper oxide, thereby obtaining cuprous oxide particles. The obtained cuprous oxide particles may also be subjected to treatments such as crushing and sieving, if necessary.

[0022] The binder resin used in one embodiment of the present invention may have a carbon molar fraction in its molecule of 0.15% to 0.9% and an oxygen molar fraction of 0.03% to 0.2%. When the carbon molar fraction and oxygen molar fraction in the binder resin molecule are within the above ranges, the cuprous oxide particles present in the surface layer of the coating film formed by applying the composition to a substrate are reduced, and the binder resin present in the surface layer is gasified and disappears, thereby forming a highly continuous, low-resistance conductive film. Meanwhile, the binder resin present in the lower layer of the coating film is more likely to remain, and this remaining binder resin is thought to improve the adhesion between the conductive film and the substrate. If the carbon molar fraction in the binder resin molecule is too small, the reduction of the cuprous oxide particles present in the surface layer of the coating film formed by applying the composition to a substrate is difficult to proceed, and increasing the light irradiation energy to proceed the reduction can result in defects such as scattering, peeling, and cracking of the conductive film. On the other hand, if the carbon molar fraction in the binder resin molecule is too large, the light irradiation energy is used to oxidize the carbon, resulting in the generation of CO and CO. ２The amount of gas increases, causing defects such as scattering, peeling, and cracking of the conductive film. In addition, if the oxygen molar fraction in the molecule of the binder resin is too small, CO and CO generated with the reduction of the cuprous oxide particles become too large. ２ This increases the amount of gas, resulting in defects such as scattering, peeling, and cracking of the conductive film. On the other hand, if the oxygen molar fraction in the binder resin molecule is too high, the reduction of the cuprous oxide particles becomes difficult to proceed, and increasing the light irradiation energy to promote the reduction will result in defects such as scattering, peeling, and cracking of the conductive film. From the perspective of improving adhesion while ensuring excellent conductivity, it is preferable that the carbon molar fraction in the binder resin molecule be 0.20% to 0.80% and the oxygen molar fraction be 0.05% to 0.18%. Note that 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 Corporation.

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

[0024] Specific examples of the binder resin include 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, and alkyd resin. These binder resins may be used alone or in combination of two or more. Since the binder resin is usually dissolved in an organic solvent, a binder resin that satisfies the carbon molar fraction and oxygen molar fraction requirements and is soluble in an organic solvent may be selected from the binder resins described above. From the viewpoints of easily forming a defect-free conductive film and further improving 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 cellulose resins include methyl cellulose, ethyl cellulose, propyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose. Examples of polyvinyl resins include polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyvinyl chloride, and polyvinylphenol. Examples of unsaturated polyester resins include those obtained by polymerizing unsaturated polyesters obtained by reacting unsaturated polybasic acids such as maleic acid, fumaric acid, and itaconic acid with polyhydric alcohols such as ethylene glycol and propylene glycol. Examples of saturated polyester resins include polyethylene terephthalate, polyethylene isodylate, and polybutylene terephthalate. Examples of terpene phenol resins include hydrogenated terpene phenol resins. Examples of acrylic resins include polymethyl(meth)acrylate, polyethyl(meth)acrylate, and polypropyl(meth)acrylate. Examples of polyether resins include polyethylene glycol and polypropylene glycol. Examples of epoxy resins include phenol novolac type epoxy resins, triphenylmethane type epoxy resins, bisphenol A type epoxy resins, biphenyl type epoxy resins, etc. From the viewpoints of facilitating the formation of 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 methyl cellulose, ethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polyethylene glycol, and polypropylene glycol.

[0026] From the viewpoints of preventing excess binder resin from remaining in the conductive film after light irradiation and facilitating ensuring adhesion between the substrate and the conductive film, the content of the binder resin is preferably 0.5% by mass to 20% by mass, and more preferably 1% by mass to 15% by mass, relative to the composition.

[0027] In one embodiment of the present invention, the composition has a viscosity of 1.0 × 10 at 20°C from the viewpoint of further improving the uniformity of the conductive film. －３ The metal particles may further contain metal particles having a volume resistivity of Ω cm or less. 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 x 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 x 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 x 10 －６ Among these metal particles, copper particles are preferred from the viewpoint of good conductivity and low cost. Two or more of these metal particles may be used in combination, or the metal particles may have a viscosity of 1.0 × 10 at 20 °C. －３ Alloy particles having a volume resistivity of Ω·cm or less may be used.

[0028] From the viewpoints of ease of handling and photosintering, the average primary particle diameter of the metal particles is preferably 10 nm to 50 μm, and more preferably 50 nm to 10 μm. The average primary particle diameter of the metal particles in one embodiment of the present invention is determined by measuring the primary particle diameters of 50 arbitrarily selected particles in an image observed with a scanning electron microscope (SEM) and calculating the arithmetic mean of these values. The shape of the metal particles is not particularly limited, and may be spherical, polyhedral, flaky, amorphous, agglomerated, or a mixture thereof.

[0029] When the composition contains the above-mentioned metal particles, from the viewpoints of suppressing an increase in the viscosity of the composition and forming a conductive film of sufficient thickness, the total content of the cuprous oxide particles and the metal particles is preferably 10% by mass to 95% by mass, and more preferably 20% by mass to 85% by mass, relative to the composition. From the viewpoints of preventing scattering during sintering, the sinterability of the conductive film, and adhesion to the substrate, the mass ratio of the metal particles to the cuprous 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 the cuprous 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 (also known as 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, and the like. Examples of organic solvents include propyl ether, butyl carbitol (also known as 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, and toluene. These organic solvents may be used alone or in combination of two or more. Among these organic solvents, terpineol and butyl carbitol are preferred from the viewpoints of drying properties and viscosity of the coating film, dispersibility of cuprous oxide particles and metal particles, solubility of the binder resin, and the like.

[0031] From the viewpoints of suppressing an increase in viscosity of the composition, ease of handling, and photosintering ability, the organic solvent is preferably contained in an amount of 5% by mass to 80% by mass, and more preferably 10% by mass to 70% by mass, based on the composition.

[0032] The composition according to one embodiment of the present invention may contain additional components in addition to 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, thixotropy-imparting agents, reducing agents, agents for improving compatibility with the substrate on which the conductive film is to be formed, and sintering aids. However, these additional components are preferably substances that volatilize during the drying process or are gasified and removed during the photo-reductive sintering process, and more preferably compounds composed of carbon, hydrogen, oxygen, and nitrogen.

[0033] The material of the substrate on which the conductive film is formed is not particularly limited, but examples include resins such as polyethylene terephthalate, polyimide, polyethylene naphthalate, etc.; 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, etc. The conductive film forming method according to one embodiment of the present invention can form a conductive film by heating at a lower temperature in a shorter time, and is therefore suitable for forming a conductive film on a paper substrate.

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

[0035] A method for forming a conductive film according to one embodiment of the present invention includes the steps of applying the above-described composition to a substrate to form a coating film, and irradiating the coating film with light to photo-reductively sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an unsintered layer between the substrate and the conductive film, the unsintered layer containing the cuprous oxide particles that have not been photo-reduced and the binder resin that has not been gasified.

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

[0037] The method for forming a conductive film according to one embodiment of the present invention preferably further comprises a step of drying the coating film after the coating film is formed. 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 baking step described below. A known dryer such as an air blower dryer or a warm air dryer can be used to dry the coating film. The drying conditions for the coating film are typically 60°C to 120°C and 5 to 60 minutes.

[0038] To reduce and sinter the cuprous oxide particles in the coating film to copper, the coating film may be irradiated with light using a known light irradiation device. Light irradiation is preferably pulsed light irradiation, from the viewpoint of easy temperature control. Pulsed light irradiation using a flash lamp is preferred, and pulsed light irradiation using a xenon (Xe) flash lamp is more preferred. Examples of devices capable of such pulsed light irradiation include the S-series xenon pulsed light irradiation device manufactured by Xenon Corporation and the Pulse Forge series light-curing device manufactured by Novacentrix. In particular, the S-2300 manufactured by Xenon Corporation not only allows for a simple pulsed light setting of voltage 1 / pulse width 1 with a single pulsed light, but also has the function of being able to continuously set voltage 2 / pulse width 2 after voltage 1 / pulse width 1 with a single pulsed light, thereby enabling continuous pulsed light irradiation in two or more steps with different conditions. As described above, the S-2300 manufactured by Zenon Corporation is suitable for reduction-sintering cuprous oxide particles because it is possible to adjust the irradiation energy for reduction-sintering. The number of steps is not particularly limited as long as it is possible to reduction-sinter the cuprous oxide particles present in the surface layer of the coating film and to leave behind the cuprous oxide particles and binder resin present in the lower layer of the coating film, and multiple steps may be set.

[0039] The irradiation energy and pulse width of the pulsed light can be appropriately selected depending 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, the thickness of the coating film, etc., so that the cuprous oxide particles present in the surface layer of the coating film can be reduced and sintered, while the cuprous oxide particles and binder resin present in the lower layer of the coating film can be left. Specifically, from the viewpoint of sufficiently reducing and sintering the cuprous oxide particles present in the surface layer of the coating film, leaving the cuprous oxide particles and binder resin present in the lower layer of the coating film, and reducing damage to the substrate, the cumulative pulsed light irradiation energy is 0.001 J / cm ２ ~100 J / cm ２ is preferably 0.01 J / cm ２ ~30 J / cm ２The pulse width of the pulsed light is preferably 1 μsec to 100 msec, and more preferably 10 μsec to 10 msec, from the viewpoints of sufficiently reducing and sintering the cuprous oxide particles present in the surface layer of the coating film, leaving the cuprous oxide particles and binder resin present in the lower layer of the coating film, and reducing damage to the substrate.

[0040] The number of pulsed light irradiations is not particularly limited as long as the cuprous oxide particles present in the surface layer of the coating film can be sufficiently reduced and sintered while the cuprous oxide particles and binder resin present in the lower layer of the coating film can be left behind, and 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 reduce and sinter the coating film by irradiation five times or less, but this is not limited depending on the type of substrate.

[0041] The atmosphere in which the pulsed light irradiation is carried out is not particularly limited, and may be any of the air atmosphere, an inert gas atmosphere, a reducing gas atmosphere, and the like.

[0042] In the conductive film forming method of the present invention, the conductive film formed on the substrate is preferably compressed to improve adhesion between the obtained conductive film and the substrate, and this compression is more preferably carried out by applying pressure with a roll. A roll press can be used for the compression. The pressure conditions for the conductive film may be determined appropriately, but from the viewpoint of improving adhesion to the substrate, a linear pressure of 100 to 30,000 kN / m is preferred.

[0043] One embodiment of the present invention includes the following. [1] A conductive film formed on a substrate, the conductive film comprising a photoreduced sintered product of a composition containing cuprous oxide particles and a binder resin, an unsintered layer containing cuprous oxide particles and binder resin that have not been photoreduced and remain between the substrate and the conductive film, and a carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9%, and an oxygen molar fraction in the molecule of the binder resin 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 its content is 150 ppm to 3000 ppm. [4] The conductive film according to any one of [1] to [3], wherein the cuprous oxide particles have an average primary particle size of 1 nm to 2000 nm. [5] The conductive film according to any one of [1] to [4], wherein the binder resin has a 50% weight loss temperature of 300°C to 500°C. [6] The conductive film according to any one of [1] to [5], wherein the binder resin comprises 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 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 conductive film according to any one of [1] to [6], wherein the composition has a volume resistivity at 20°C of 1.0 x 10 －３The conductive film according to any one of [1] to [7], further comprising metal particles having a resistivity of Ω cm or less. [9] The conductive film according to [8], wherein the metal particles are particles of at least one type of metal 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, comprising: a step of applying a composition containing cuprous oxide particles and a binder resin to the substrate to form a coating film; and a step of irradiating the coating film with light to photo-reductively sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an unsintered layer between the substrate and the conductive film, the unsintered layer containing the cuprous oxide particles and binder resin that remain unphoto-reduced; 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

[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.

[0044] The present invention will be described below with reference to 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 solution of sodium hydroxide and 100.0 g of pure water were added to a 500 mL reaction vessel, and the temperature in the reaction vessel was adjusted to 40 ° C. while stirring the contents in the reaction vessel to prepare an alkaline solution. Meanwhile, 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 in 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] 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. This reducing agent solution was added to a reaction vessel over approximately 30 seconds, and then the temperature inside the reaction vessel was raised to 50°C and maintained 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 1.

[0047] The average primary particle diameter of the obtained cuprous oxide particles 1 was determined to be 0.1 μm from an image of the obtained cuprous oxide particles 1 observed by an electron microscope (SEM). The tin content of the cuprous oxide particles 1 was 570 ppm.

[0048] Examples 1 to 10, Comparative Examples 1 to 4 Using the cuprous oxide particles 1 obtained above, compositions were prepared and conductive films were formed. Specifically, cuprous oxide particles 1, a binder resin, and butyl carbitol as an organic solvent were kneaded in the proportions shown in Table 1 using a kneader at 1,000 rpm under atmospheric pressure for 30 minutes to prepare paste compositions. The paste composition was screen-printed onto a paper substrate (SWORD, manufactured by Mitsubishi Paper Mills, 50 μm thick) to form a 1 mm x 20 mm rectangular pattern, forming a coating film. The coating film was dried at 80°C for 10 minutes in an atmospheric atmosphere. A conductive film was formed by irradiating the coating film formed on the paper substrate with one pulse of pulsed light (voltage: 2700 V, pulse width: 2000 microseconds) using a xenon pulsed light irradiation device (S-2300, manufactured by Zenon Corporation) so that the pulsed light irradiation energy was the value shown in Table 1. Next, the conductive film together with the substrate was passed through a roll press (steel rolls with a diameter of 60 mm) at a linear pressure of 1000 kN / m and a roll peripheral speed of 10 mm / s, thereby carrying out a compression treatment. However, in Comparative Example 4, the fluororesin used as the binder resin was not dissolved in the organic solvent, so a coating film could not be formed.

[0049]

[0050] <Preparation of Cuprous Oxide Particles 2> 25.0 g of a 48% by mass aqueous solution of sodium hydroxide and 100.0 g of pure water were added to a 500 mL reaction vessel, and the temperature in the reaction vessel was adjusted to 40 ° C. while stirring the reaction vessel to prepare an alkaline solution. Meanwhile, 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 in 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] 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. This reducing agent solution was added to the reaction vessel over approximately 30 seconds, and then the temperature inside the reaction vessel was raised to 50°C and maintained for 15 minutes. Thereafter, stirring in 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 from an image of the obtained cuprous oxide particles 2 observed with an electron microscope (SEM) to be 0.1 μm. The manganese content of 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, compositions were prepared and conductive films were formed. Specifically, cuprous oxide particles 2, copper particles (1100Y, manufactured by Mitsui Mining & Smelting Co., Ltd., average particle size 1.1 μm), a binder resin, and butyl carbitol as an organic solvent were kneaded in the proportions shown in Table 2 using a kneader at 1,000 rpm for 30 minutes under atmospheric pressure to prepare paste compositions. The paste compositions were screen printed onto a polyethylene terephthalate substrate (Lumirror S10, manufactured by Toray Industries, Inc., thickness 50 μm) in a 1 mm x 20 mm rectangular pattern to form a coating film. The coating film was dried at 80°C for 10 minutes in an atmospheric atmosphere. A conductive film was formed by irradiating the coating film formed on the polyethylene terephthalate substrate with one pulse of pulsed light (voltage: 2700 V, pulse width: 2000 microseconds) using a xenon pulsed light irradiation device (S-2300 manufactured by Zenon Corporation) so that the pulsed light irradiation energy was the value shown in Table 2. Next, a compression treatment was performed by passing the conductive film together with the substrate between roll presses (steel rolls with a diameter of 60 mm) at a linear pressure of 1000 kN / m and a roll peripheral speed of 10 mm / s.

[0054]

[0055] <Printability Evaluation> A wiring pattern was printed on a substrate by screen printing, and the printed matter was observed under a microscope and evaluated for appearance according to the following criteria. A wiring pattern without any defects was judged to have "excellent" printability, a wiring pattern with some defects was judged to have "good" printability, and a wiring pattern with breaks or bleeding was judged to have "poor" printability. The results are shown in Table 3.

[0056] <Evaluation of sinterability> A conductive film formed that was uniform and free of defects was judged to have "excellent" sinterability, a conductive film with some defects due to scattering of the conductive film or with some unsintered portions was judged to have "good" sinterability, and a conductive film with defects due to scattering or an unsintered portion was judged to have "poor" sinterability. The results are shown in Table 3.

[0057] <Adhesion Evaluation> After applying tape to the formed conductive film, the tape was peeled off. If the conductive film was not attached to the adhesive surface of the tape and the conductive film formed on the paper substrate remained intact, the adhesion was judged to be "excellent." If the conductive film was attached to part of the adhesive surface of the tape but there were no breaks in the conductive film, the adhesion was judged to be "good." If the conductive film was attached to the adhesive surface of the peeled tape and the conductive film was broken, the adhesion was judged to be "poor." The results are shown in Table 3.

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

[0059]

[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 poor adhesion to the substrate.

Claims

1. A conductive film formed on a substrate, the conductive film being made of a photoreduced and sintered product of a composition containing cuprous oxide particles and a binder resin, an unsintered layer containing cuprous oxide particles and binder resin that have not been photoreduced and remain between the substrate and the conductive film, and a carbon molar fraction in the molecule of the binder resin is 0.15% to 0.9%, and an 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. 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 size of 1 nm to 2000 nm.

5. The conductive film according to claim 1 or 2, wherein the binder resin has a 50% weight loss temperature of 300°C to 500°C.

6. The conductive film according to claim 1 or 2, wherein the binder resin comprises 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 claim 1 or 2, 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 at 20° C. －３ The conductive film according to claim 1 or 2, further comprising metal particles having a resistivity of Ω·cm or less.

9. The conductive film according to claim 8, wherein the metal particles are particles of at least one type of metal 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: 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 photo-reduce and sinter the cuprous oxide particles in the coating film to form a conductive film, while forming an unsintered layer between the substrate and the conductive film, the unsintered layer containing the cuprous oxide particles and binder resin that have not been photo-reduced, the binder resin 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 of the conductive film.

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 subjecting the conductive film formed on the substrate to a compression treatment.

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