JP2015069750A - Conductive paste, method for producing metallic thin film, and metallic thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive paste capable of producing a conductive metallic thin film by a firing method with super heat steam treatment, whose firing temperature can be reduced, and even widely applicable to a base material having no heat resistance.SOLUTION: Provided is conductive paste for super heat steam treatment containing metallic nanoparticles protected with a hydrolyzable protective agent, and also provided is a method for producing a metallic thin film in which a coating film is formed using the conductive paste, and the coating film is subjected to heating treatment with super heat steam to obtain a metallic thin film.

Description

  TECHNICAL FIELD The present invention relates to a conductive paste containing specific metal nanoparticles, and a low specific resistance metal thin film excellent in conductivity, which is produced by a heat treatment using superheated steam for a coating film formed using the conductive paste.

  In recent years, a technique of forming a desired pattern by a printing method such as a screen printing method using a conductive paste containing a metal fine particle dispersion and forming a wiring or the like on a circuit board has attracted attention.

  In the conductive paste, silver, copper, or nickel is generally used as the metal as the metal fine particles. Silver is not only expensive, but also has poor migration resistance, and can be a serious defect when there is a high demand for circuit miniaturization. Nickel has poor conductivity. Since copper is inexpensive and has good migration resistance, it is expected to exhibit excellent characteristics as metal fine particles for conductive paste. However, copper is easily oxidized, and the resulting oxide has poor conductivity. The conductivity deteriorates due to the oxide layer formed on the copper surface at the time of heat treatment when forming a copper thin film from the conductive copper paste and at the time of storage of the copper thin film during production and storage of the conductive copper paste.

  A method for treating a conductive copper paste coating film containing copper fine particles in a reducing atmosphere is disclosed. In addition to the well-known heat treatment in nitrogen gas containing 3% of hydrogen gas (Non-patent Document 1), several methods are disclosed. For example, in the microwave surface wave plasma treatment (Patent Document 1), the thickness of the coating film that can be treated is limited to 2 μm or less. Further, the treatment with gaseous formic acid and / or formaldehyde (Patent Document 2) can be carried out at a low temperature of 200 ° C. or less, but there are concerns about the toxicity of formic acid gas and formaldehyde gas and the difficulty of treatment with a thick coating film.

  There has been disclosed a photosintering method in which only a coating film containing copper oxide is heated to form a copper coating without irradiating high-energy pulse light and raising the temperature of the substrate. (For example, Patent Document 3) Although this method has an advantage that it can be processed at room temperature in a short time, there is a problem that an irradiation apparatus is expensive and conditions for not damaging the substrate are narrow.

  Furthermore, a method of applying pressure during heating and baking is disclosed. For example, Patent Document 4 and Patent Document 5 disclose a method of forming a conductive film by heat-treating a dispersion of conductive fine particles and then applying pressure while heating. These methods are advantageous in terms of cost and are easy to sinter with silver particles, but in the case of copper particles, the oxidation reaction proceeds easily during heating and pressurization, and the oxide film on the particle surface sinters. Therefore, a film having high conductivity cannot be obtained.

  Patent Document 6 discloses a method of obtaining a copper film by placing a shielding object directly on a coating film containing copper particles and subjecting it to heat and pressure treatment. In this method, the reaction with oxygen in the outside air can be suppressed to some extent, but there is a limit, and if the shield cannot be recycled, a problem of waste arises.

  In Patent Document 7, by applying a conductive paste using copper as a conductive powder to a base material and then performing a superheated steam treatment, it is in a lower oxygen state than in a firing treatment in the atmosphere, and more than air. By using water vapor having a large specific heat capacity, heat-firing can be performed safely and in a short time, and thus a technique has been disclosed in which the specific resistance of a coated metal thin film can be reduced.

  It is known that by reducing the particle size of the metal particles, the firing temperature between the metal particles can be significantly reduced compared to the melting point of the metal bulk. When the average particle size of metal fine particles is about several nanometers to several tens of nanometers, the melting point of the metal particles is significantly lower than that of bulk metal, and the particles are fused at a low temperature. Thus, a conductive thin film is obtained.

  In a copper paste containing copper particles, when trying to cause a melting point decrease due to a reduction in the particle size of the copper fine particles, the copper fine particles are easily oxidized, and the tendency becomes more remarkable in the case of copper nanoparticles having a nano-size particle size. , Face problems with. Since the conductivity of the oxidized copper fine particles is remarkably lowered, it is a big problem to suppress oxidation while maintaining dispersibility in order to use as a conductive copper paste.

  In order to solve such problems, protective agents have been studied. Here, the protective agent covers copper fine particles by using adsorption to copper metal, thereby preventing contact between the copper fine particles and oxygen or water, preventing oxidation of the copper fine particles and at the same time aggregating the copper fine particles with each other. Refers to those that have a function of suppressing dispersibility and maintaining dispersibility. For example, some compounds having such a function are present in compounds having a heteroatom such as a nitrogen atom or an oxygen atom in the molecular structure.

  In addition, when forming a conductive pattern using a dispersion containing copper fine particles coated with such a protective agent, in order to ensure good conductivity, a protective agent adsorbed on the copper fine particles is used. It is necessary to decompose and / or desorb and bring the copper fine particles into sufficient contact with each other to promote fusion. However, until now, much consideration has not been given to the decomposability and detachability of the protective agent, and deprotection does not proceed sufficiently in the firing step, and the formed wiring may not be able to ensure good conductivity.

  A technique for improving the conductivity by deprotecting a polymer protective agent adsorbed and coated on copper fine particles during firing has been disclosed. For example, Patent Document 8 discloses a conductive paste containing metal nanoparticles using a polymer such as polyalkyleneimines as a protective agent and an aliphatic monocarboxylic acid as a deprotecting agent. The protective agent that coats the surface of the metal nanoparticles is desorbed by the action of the deprotecting agent during firing to expose the metal surface, and the metal nanoparticles are sintered together at a relatively low temperature. However, since the action of the deprotecting agent occurs little by little even at room temperature, there is a concern that the storage stability of the conductive paste may deteriorate.

  Patent Document 9 discloses the use of a heat-decomposable or ultraviolet-degradable protective agent. However, there is a concern that a specially structured polymer must be used. Patent Document 10 proposes to use a photoacid generator or a photobase generator as a deprotecting agent. Patent Document 11 proposes the use of a proteolytic enzyme as a deprotecting agent for metal fine particles coated with a protein protecting agent. All of these have problems in practicality in terms of process conditions.

JP 2010-192841 A International Publication No. 2011/0334016 Pamphlet International Publication No. 2006/071419 Pamphlet JP 2005-177710 A JP 2008-124446 A JP 2010-146734 A Japanese Patent No. 4835590 Japanese Patent No. 4835810 JP 2009-170419 A JP 2013-10977 A JP 2005-89597 A

Nakagomi et al., “Electronic circuit formation with new copper nanoparticle paste”, MES 2006 16th Microelectronics Symposium Proceedings, October 2006, p. 51

  The present invention has been made against the background of such prior art problems. That is, an object of the present invention is to provide a conductive metal thin film that can be produced by a baking method using a superheated steam treatment, that can lower the baking temperature, and that can be widely applied to substrates that do not have heat resistance. Is to provide a sex paste.

As a result of intensive studies to achieve this object, the present inventor has found that the above-mentioned problems can be solved by the following means, and has reached the present invention. That is, the present invention
(1) A conductive paste for superheated steam treatment containing metal nanoparticles protected with a hydrolyzable protective agent.
(2) The conductive paste according to (1), wherein the hydrolyzable protective agent is a protein.
(3) The conductive paste according to (1) or (2), wherein the metal nanoparticle contains particles made of at least one of copper, copper oxide, and copper complex.
(4) The conductive paste according to any one of (1) to (3), wherein a heat treatment temperature in the superheated steam treatment is 200 ° C. or higher.
(5) Production of a metal thin film, wherein a coating film is formed using the conductive paste according to any one of (1) to (4), and then the coating film is heated with superheated steam to obtain a metal thin film. Method.
(6) A metal thin film produced by the production method of (5).

  By using the conductive paste of the present invention and the method for producing a metal thin film of the present invention, a conductive metal thin film can be produced by a firing method by superheated steam treatment, the firing temperature can be lowered, and heat resistance is ensured. Thus, it is possible to provide a conductive paste that can be widely applied to a substrate that does not.

Hereinafter, the present invention will be described in detail.
In the present invention, an extremely conductive metal thin film can be obtained by subjecting a coating film formed using a conductive paste containing metal nanoparticles protected with a protective agent to heat treatment with superheated steam. It is preferable that the hydrolyzable protective agent is a protein, and the coating film is obtained by applying or printing a metal nanoparticle dispersion on an insulating substrate.

  In the present invention, the heat treatment with superheated steam makes the treatment atmosphere oxygen-free or low-oxygen, and even metal fine particles that easily oxidize in the air, such as copper nanoparticles, are oxidized in the heat treatment step. This can be suppressed. As a result, the deterioration of conductivity due to oxidation hardly occurs.

  In this invention, a metal thin film is manufactured by performing the heat processing by superheated steam to the coating film formed using the electrically conductive paste containing a metal nanoparticle. It is preferable that the coating film is obtained by applying or printing a conductive paste containing metal nanoparticles on an insulating substrate.

  The metal nanoparticle-containing conductive paste of the present invention is obtained by dispersing metal nanoparticles in a dispersion medium and may contain a binder resin if necessary.

  The average particle diameter of the metal nanoparticles used in the present invention is preferably 1 nm or more and 1000 nm or less, and more preferably 1 nm or more and 100 nm or less. The average particle diameter is measured by measuring the particle diameter of 100 particles using any one of a transmission electron microscope, a field emission transmission electron microscope, and a field emission scanning electron microscope to obtain an average value.

  If the average particle size of the metal nanoparticles is large, the melting point lowering phenomenon of the metal nanoparticles cannot be expected, so that sintering at a low temperature cannot be performed. Moreover, sedimentation of the metal nanoparticles in the conductive paste occurs, and the printability of the fine circuit is inferior. The lower limit of the average particle size is not particularly limited, but a large amount of protective agent and dispersion medium are required to limit the economic efficiency of metal nanoparticles and obtain a stable dispersion. It may be difficult to obtain. The metal nanoparticles used in the present invention may be used by mixing different particle sizes.

  As the metal nanoparticles used in the present invention, either metal nanoparticles fused by heat treatment or those not fused can be used. As a kind of metal used for the metal nanoparticle used by this invention, copper, nickel, cobalt, silver, platinum, gold | metal | money, molybdenum, titanium etc. can be mentioned, Especially copper is preferable. Moreover, the metal nanoparticles in the present invention contain particles composed of one or more of metals, metal oxides, metal complexes, and metal alloys, and include copper nanoparticles, copper oxide nanoparticles, and copper complex nanoparticles. Particles containing one or more of these are particularly preferred. In addition, metal nanoparticles with a part or all of the surface covered with metal, metal oxide, metal complex and metal alloy, a structure in which different kinds of metals are laminated, or organic or inorganic materials plated with metal may be used. Absent. A commercial item may be used for these metal nanoparticles, and it can also be prepared using a well-known method.

  The protective agent used in the present invention is to coat metal nanoparticles using adsorption to metal, thereby preventing contact between metal nanoparticles and oxygen or water, and at the same time preventing oxidation of metal nanoparticles. , Refers to those that have the function of suppressing the aggregation of metal nanoparticles and maintaining the dispersibility. For example, some compounds having such a function are present in compounds having a heteroatom such as a nitrogen atom or an oxygen atom in the molecular structure.

  The hydrolyzable protective agent in the present invention refers to those having hydrolyzability while exhibiting the function as the above-described protective agent. The hydrolyzability required for the hydrolyzable protective agent of the present invention refers to a substance that decomposes into low molecules by hydrolysis on the surface of metal nanoparticles during heat treatment with superheated steam. It is possible to carry out the metal nanoparticle production process and the conductive paste production process in the presence of a hydrolyzable protective agent. It is necessary to select a hydrolyzable protective agent that has. The necessary degree of hydrolyzability depends on conditions such as acidity, basicity, and temperature in these steps, in addition to the firing temperature with superheated steam.

  The hydrolyzable protective agent is preferably a compound containing a chemical structure having a hetero atom such as a nitrogen atom or an oxygen atom that is easily adsorbed on the surface of the metal nanoparticle, and examples thereof include proteins, cellulose derivatives, and natural polymers. . Among these, proteins containing a carboxyl group or an amino group and having an amide bond (peptide bond) as the main chain are preferred, and examples thereof include gelatin, casein, casein soda, and ammonium caseinate.

  In the conductive paste of the present invention, an acidic substance can be contained in order to promote the hydrolysis reaction of the protective agent, and examples thereof include organic acids, inorganic acids, and precursors thereof. As an acid precursor, the thermal acid generator which produces | generates an acidic substance with the heat | fever at the time of baking is preferable. Examples of the thermal acid generator include pyridinium derivatives, sulfonium derivatives, sulfonic acid esters and the like. Further, in the conductive paste of the present invention, a basic substance can be contained in order to promote the hydrolysis reaction of the protective agent, and examples include organic bases, inorganic bases, and precursors thereof. . As the base precursor, a thermal base generator that generates a basic substance by heat during firing is preferable. Examples of thermal base generators include carbamate derivatives and guanidine derivatives.

  The conductive paste of the present invention can contain a reducing agent. A reducing agent means what has the capability to reduce | restore metal compounds, such as a metal oxide, a hydroxide, or a salt, to a metal. Examples of the reducing agent include sodium borohydride, lithium borohydride, hydrazines, aldehydes such as formalin and acetaldehyde, sulfites, formic acid, succinic acid, carboxylic acids such as succinic acid and ascorbic acid, or lactones, ethanol, Aliphatic monoalcohols such as butanol and octanol, monoalcohols such as alicyclic monoalcohols such as terpineol, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, glycerin and trimethylolpropane, Polyethers such as polyethylene glycol and polypropylene glycol, alkanolamines such as diethanolamine and monoethanolamine, hydroquinone, resorcinol, glucose, or Sodium citrate, and the like. Residue of the reducing agent or the reducing agent decomposition product on the metal thin layer may cause deterioration of properties such as conductivity of the obtained metal thin layer and adhesion to the insulating substrate. Therefore, it is desirable that the reducing agent is evaporated by superheated steam treatment. In addition, when the coating layer of the metal fine particle dispersion is subjected to the superheated steam treatment, it is desirable that the reducing agent remains in the coating layer. Therefore, when the reducing agent is a liquid volatile substance, the boiling point is desirably 150 ° C. or higher. As the reducing agent of the present invention, alcohols and polyhydric alcohols are desirable. Specific preferred examples of the reducing agent of the present invention include terpineol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, ascorbic acid, resorcinol and the like.

  The conductive paste of the present invention usually comprises metal nanoparticles protected with a hydrolyzable protective agent and a solvent. The solvent is not particularly limited as long as the metal nanoparticles protected with the hydrolyzable protective agent can stably exist in a dispersed state, and examples thereof include alcohols, ethers, ketones, esters, aromatic hydrocarbons, amides, and the like. It is done. A solvent in the range of 20 to 400 parts by weight is preferably blended with 100 parts by weight of the metal fine particles. Furthermore, a binder can also be mix | blended in 3-15 weight part.

  In the case of using a binder, the solvent used in the conductive paste of the present invention is preferably selected from those that dissolve the binder, and may be an organic compound or water. The solvent has a role of adjusting the viscosity of the conductive paste in addition to the role of dispersing the metal nanoparticles in the conductive paste. Examples of the organic solvent suitably used as a solvent in the case of using a binder include alcohol, ether, ketone, ester, aromatic hydrocarbon, amide and the like.

  Examples of the binder that can be used in the conductive paste of the present invention include polyester, polyurethane, polycarbonate, polyether, polyamide, polyamideimide, polyimide, and acrylic.

  When the electrically conductive paste of this invention contains a binder, you may mix | blend the hardening | curing agent which has reactivity with respect to a binder as needed. Examples of the curing agent that can be used in the conductive paste of the present invention include phenol resins, amino resins, isocyanate compounds, and epoxy resins. The amount of the curing agent used is preferably in the range of 1 to 100% by weight of the binder resin, and the effect of improving the adhesion and surface hardness of the coating film may be exhibited.

  The metal nanoparticles protected with the hydrolyzable protective agent used in the present invention can be produced by bringing the hydrolyzable protective agent and the metal nanoparticles into contact with each other. For example, a method of adding and mixing a hydrolyzable protective agent to metal nanoparticles dispersed in a liquid phase can be mentioned. However, the above method requires an expensive and complicated apparatus to prevent the influence of oxygen and water, and has an industrial problem. Therefore, a method of contacting the metal nanoparticles with a hydrolyzable protective agent at the same time is preferable.

  In the method for obtaining metal nanoparticles protected with the hydrolyzable protective agent of the present invention, the synthesis of the metal nanoparticles is not particularly limited, and any known method can be used. A method of reducing and depositing metal nanoparticles after mixing the particle precursor is preferred. The deposited metal nanoparticles can be redispersed in a solvent, and an additive can be mixed as necessary to produce a conductive paste.

  The hydrolyzable protective agent in the present invention is preferably prepared so as to be in the range of 1 to 5% in terms of non-volatile content with respect to the metal nanoparticles. With such a range, the surface of the metal nanoparticles does not come into contact with moisture or oxygen, and the metal nanoparticles do not self-fuse, so that sufficient protection can be achieved without excess and deficiency, and superheated steam This is preferable in that it is not necessary to make the conditions of the processing temperature and processing time strict.

  In order to form a coating film using the conductive paste of the present invention, a general method used when applying or printing the conductive paste on an insulating substrate can be used. For example, the conductive paste of the present invention is applied or printed by a method such as a screen printing method, a dip coating method, a spray coating method, a spin coating method, a roll coating method, a die coating method, an ink jet method, a relief printing method, an intaglio printing method, Next, the coating film can be formed by evaporating at least a part of the dispersion medium by air drying, heating, or reduced pressure. The coating film may be provided on the entire surface of the insulating substrate or may be provided partially, or may be a pattern formed product such as a conductive circuit.

  The thickness of the metal thin film of the present invention can be appropriately set according to necessary characteristics such as electric resistance and adhesiveness, and is not particularly limited. Although the range of the thickness of the metal thin film that can be formed varies depending on the composition of the conductive paste and the method of application or printing, it is preferably 0.05 to 20 μm, more preferably 0.1 to 15 μm, still more preferably 0.2 to 10 μm. In order to obtain a thick metal thin film, it is necessary to increase the thickness of the coating film, which is likely to cause economic deterioration such as an adverse effect due to residual solvent and a need to reduce the coating film forming speed. On the other hand, if the coating film is too thin, the occurrence of pinholes tends to be significant.

  When forming the metal thin film of the present invention, it is possible to perform overprinting or multilayer printing. Here, overprinting refers to printing the same pattern a number of times, thereby increasing the thickness of the metal thin film or having a high aspect ratio (ratio of film thickness to line width). Can be obtained. Multi-layer printing refers to printing different patterns in a superimposed manner, whereby different functions can be exhibited for each layer. Partial overprinting and / or multilayer printing may be performed, and overprinting and multilayer printing may be performed in combination. It is also possible to perform multilayer printing with a thin film different from the metal thin film of the present invention, such as an insulating layer.

  A metal thin film can be produced by forming a coating film using the conductive paste of the present invention and then subjecting the coating film to heat treatment with superheated steam. Superheated steam is high-temperature steam heated to several hundred degrees by adding secondary energy to saturated steam. Superheated steam has a heat capacity approximately four times that of air at the same temperature, and it is known that when heated with superheated steam, the substance is heated in a short time. When the superheated steam treatment is performed without applying a drying step after coating, the volatile components contained in the coating film may bump out and the uniformity of the coating film may deteriorate. The drying process and the superheated steam process may be performed continuously or may be performed with another process interposed therebetween. Examples of the process sandwiched between the drying process and the superheated steam process include a process of applying a reducing agent to the coating film. In this case, the coating film may or may not contain a reducing agent in advance, and if it is contained, any of the same type, different type, and a mixture of the same type and different type It is also possible to do. By the treatment of applying a reducing agent to the coating film, effects such as a decrease in volume resistivity of the coating film, a decrease in overheat treatment temperature, and a decrease in overheat treatment time may be exhibited.

  In the coating film formed using the conductive pace of the present invention, the metal nanoparticles are protected with a hydrolyzable protective agent. When the coating is heated with superheated steam, the hydrolyzable protective agent on the surface of the metal nanoparticles is hydrolyzed and desorbed as low molecules due to the action of water in the superheated steam at high temperature, Volatilizes to expose the metal nanoparticle surface. Therefore, metal nanoparticles can be easily fused together, and a metal film having excellent conductivity can be obtained.

  In the present invention, superheated steam containing an alcohol compound can be used as superheated steam. Alcohol compounds to be included in superheated steam are aliphatic monoalcohols such as methanol, ethanol, 1-propanol and 2-propanol, monoalkyls of aliphatic diols such as ethylene glycol monoethyl ether, ethylene glycol monoethyl ether and propylene glycol monomethyl ether Monoalcohol compounds such as ether, cyclohexanol, terpineol, and other alicyclic monoalcohols, aliphatic diols such as ethylene glycol, propylene glycol, diethylene glycol, and butanediol, alicyclic diols such as cyclohexanedimethanol, glycerin, and trimethylolpropane And polyhydric alcohol compounds such as pentaerythritol, and hydroxycarboxylic acids such as tartaric acid, hydroxybutyric acid and malic acid. Of these, methanol, ethanol, ethylene glycol, and propylene glycol are preferred.

  Examples of a method for producing superheated steam containing an alcohol compound include a method of heating saturated steam of a solution in which an alcohol compound is dissolved in water, and a method of mixing and heating each saturated steam of an alcohol compound and water. The content of the alcohol compound in the superheated steam is preferably in the range of 0.01 to 20% by weight, although the optimum range varies depending on the type of compound. When the content of the alcohol compound is less than 0.01% by weight, the effect of improving the conductivity is not observed, and when it exceeds 20% by weight, the binder resin may be significantly dissolved or decomposed. A more preferable range is 0.1 to 5% by weight.

  The temperature of the superheated steam used in the present invention is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and particularly preferably 250 ° C. or higher. As the temperature rises, the specific resistance of the formed metal thin film tends to decrease. The upper limit of the temperature is preferably 500 ° C. or less. The upper limit of the temperature is also limited by the heat resistance characteristics of the insulating substrate and binder resin used. The heating time is also selected from the amount and characteristics of the object to be processed, but is preferably 10 seconds to 30 minutes. If the temperature of the superheated steam is too low, a metal film having a low specific resistance cannot be obtained. If the temperature of the superheated steam is too high, the adhesion between the metal thin film and the insulating substrate may be impaired, and the insulating substrate may be deteriorated, so care must be taken.

  The heat treatment operation with superheated steam can be handled in the same manner as the heat treatment operation with heated air in hot air drying. When air is completely replaced with superheated steam, an oxygen-free state similar to that of an inert gas is obtained, and an oxidation reaction can be prevented.

  In this invention, when a metal thin film is a copper thin film, it is preferable to give a rust prevention process. As a preferable antirust treatment method, a method of providing an adsorption layer of an organic compound or an inorganic compound capable of adsorbing copper on the surface of the copper thin film layer can be mentioned. Here, when the copper particles contained in the copper thin film layer contain copper particles that are not fused to each other, the adsorption layer is preferably formed on the surface of each copper fine particle. Another preferred rust prevention treatment method is a method of providing a waterproof insulating resin layer on the copper thin film layer. The method of providing an organic compound or inorganic compound adsorption layer on the surface of the copper thin film layer, and further covering with an insulating resin layer is an example of a preferred embodiment of the present invention.

  Examples of the organic compound or inorganic compound (hereinafter sometimes referred to as a surface treating agent) capable of forming an adsorption layer on the surface of the copper thin film layer in the present invention include nitrogen-containing heterocyclic compounds such as benzotriazole, tolyltriazole, and tetrazole, mercapto Examples thereof include sulfur-containing compounds such as propionic acid, mercaptoacetic acid, thiophenol and triazinedithiol, amino compounds such as octylamine and isobutylamine, silane coupling agents, titanium coupling agents and chromate treatment agents. The adsorption layer is formed by immersing the copper thin film in the treatment agent in which the surface treatment agent is dissolved or by applying the treatment agent to the copper thin film. When the thickness of the surface treatment agent layer is increased, the conductivity may be lowered or the adhesive processability may be deteriorated. Therefore, the thickness of the surface treatment layer is preferably a thin layer of 0.05 μm or less. Examples of the method for thinning the surface treatment agent layer include reducing the concentration of the treatment liquid and removing excess surface treatment agent with a solvent that dissolves the surface treatment agent.

  A layer made of a waterproof insulating resin can be provided on the copper thin film layer in the present invention. Examples of the waterproof resin include polyester resin, acrylic resin, polyurethane resin, butyral resin, and the like. By coating the copper thin film layer with one or more of these resins, the antirust effect can be exhibited. The method of coating the copper thin film layer with a waterproof insulating resin is not particularly limited, but the method of coating or printing the resin solution on the copper thin film layer and then stripping off the solvent, applying the adhesive to the resin film and applying the adhesive to the copper thin film layer The method of bonding to can be illustrated as a preferable method. Bonding a polyimide film or a polyester film with an adhesive is an example of a particularly preferred embodiment. The thickness of the insulating resin layer is desirably 1 to 30 μm.

  The insulating substrate used in the present invention may be either an organic material or an inorganic material. Examples of the material used for the insulating substrate include glass, ceramics, polyimide resin, and tetrafluoroethylene resin. Moreover, composite articles, such as a glass epoxy board | substrate, a paper epoxy board | substrate, and a paper phenol board | substrate which are normally used for an electrical wiring circuit board, are also mentioned. In the present invention, since heat treatment with superheated steam is performed, it is essential to have heat resistance that can withstand this. For this reason, it is preferable to use a film, sheet, or ceramic made of a polyimide resin having excellent heat resistance as an insulating substrate.

  In order to describe the present invention in more detail, examples are given below, but the present invention is not limited to the examples. In addition, the measured value described in the Example is measured by the following method.

1. Measurement of electrical resistivity (specific resistance) The electrical resistivity was measured by a four-terminal method using a low resistivity meter (trade name: Loresta CP, manufactured by Mitsubishi Chemical) and a four-probe probe (NSCP probe).

2. Measurement of the particle size of copper nanoparticles Measured with a transmission electron microscope (TEM) “JEM1200EX” (manufactured by JEOL Ltd.), the arithmetic average value of the diameter of 200 arbitrarily selected particles is obtained, and the value is used as the particle size. did.

Production example 1 of copper nanoparticles
Pure water of 300 ml of 24 g of industrial cupric oxide (N-120: manufactured by NC Tech) with an average crystallite size of 90.2 nm and 9.6 g of gelatin (cow bone-derived product, Wako Pure Chemical) as a protective agent The mixture was adjusted to pH 11 with 15% aqueous ammonia and then heated from room temperature to 90 ° C. over 20 minutes. After the temperature rise, with stirring, a solution prepared by mixing 2 g of a 1% solution of 3-mercaptoacetic acid and 28 g of 80% hydrazine monohydrate in 150 ml of pure water was added, and the second oxidation was performed over 1 hour. Reaction with copper produced copper fine particles. Thereafter, the filtrate was washed by filtration until the specific conductivity of the filtrate reached 100 μS / cm or less, dried in a nitrogen gas atmosphere at a temperature of 60 ° C. for 10 hours, and protected with gelatin nanoparticles A (particle size 80 nm) Got. The nonvolatile content was 4.8% by weight.

Production example 2 of copper nanoparticles
Protected with polyvinylpyrrolidone in the same manner as in copper nanoparticle production example 1 except that polyvinylpyrrolidone (trade name: polyvinylpyrrolidone K-30, manufactured by Nippon Shokubai Co., Ltd., viscosity average molecular weight 40000) is used instead of the protective agent gelatin. Copper nanoparticles B (particle size 70 nm) were obtained. The nonvolatile content was 4.4% by weight.

Example 1
To 1.0 g of copper nanoparticles A, 5.6 g of terpineol and 20 g of toluene were added and stirred at 60 ° C. for 1 hour to redisperse the copper nanoparticles. This uniform dispersion was filtered through a 0.5 μm membrane filter, and then toluene in the filtrate was removed by concentration under reduced pressure to prepare a conductive copper paste 1.

Comparative Example 1
To 1.0 g of copper nanoparticles B, 5.6 g of terpineol and 20 g of toluene were added and stirred at 60 ° C. for 1 hour to redisperse the copper nanoparticles. The uniform dispersion was filtered through a 0.5 μm membrane filter, and then the toluene in the filtrate was removed by concentration under reduced pressure to prepare a conductive copper paste 2.

Example 2
The conductive copper paste 1 obtained in Example 1 was applied onto a polyimide film using a bar coater and dried with hot air at 120 ° C. for 5 minutes to obtain a dried coating film having a thickness of 5 μm. Then, the baking process by superheated steam for 60 minutes at 200 degreeC was performed. The specific resistance of the obtained copper thin film is shown in Table 1. In the baking process using superheated steam, a steam superheater (“DHF Super-Hi 10” manufactured by Daiichi High Frequency Industrial Co., Ltd.) is used as a superheated steam generator, and 10 kg / hour of superheated steam is supplied to the heat treatment furnace. went.

Examples 3-4
Instead of 200 ° C, the firing temperature was 250 ° C (Example 3) and 300 ° C (Example 4), and a copper thin film was obtained in the same manner as in Example 2 except that the firing time was 10 minutes. The specific resistance of the obtained copper thin film is shown in Table 1.

Example 5
A copper thin film was obtained in the same manner as in Example 3 except that the firing time was 1 hour instead of 10 minutes. The specific resistance is shown in Table 1.

Comparative Example 2
The conductive copper paste 2 obtained in Comparative Example 1 was applied onto a polyimide film using a bar coater and dried with hot air at 120 ° C. for 5 minutes to obtain a 5 μm coating film. In the same manner as the baking process using heated steam in Example 2, baking process using superheated steam at 200 ° C. for 60 minutes was performed. The specific resistance of the obtained copper thin film is shown in Table 1.

Comparative Example 3
A copper thin film was obtained in the same manner as in Comparative Example 2 except that the firing temperature and firing time were set at 250 ° C. for 10 minutes. The specific resistance of the obtained copper thin film is shown in Table 1.

Comparative Example 4
A copper thin film was obtained in the same manner as in Example 2 except that the firing temperature was 150 ° C. The specific resistance of the obtained copper thin film is shown in Table 1.

Comparative Example 5
The conductive copper paste 1 obtained in Example 1 was applied onto a polyimide film using a bar coater and dried with hot air at 120 ° C. for 5 minutes to obtain a 5 μm coating film. Subsequently, a baking treatment was performed at 250 ° C. for 10 minutes in a hydrogen-nitrogen mixed atmosphere having a hydrogen content of 5% by volume. The specific resistance of the obtained copper thin film is shown in Table 1.

Comparative Example 6
Table 1 shows the specific resistance of the copper thin film obtained in the same manner as in Comparative Example 5 except that the firing time was 60 minutes.

Comparative Example 7
The conductive copper paste 1 obtained in Example 1 was applied onto a polyimide film using a bar coater and dried with hot air at 120 ° C. for 5 minutes to obtain a 5 μm coating film. Subsequently, a baking treatment was performed at 250 ° C. for 10 minutes in a nitrogen mixed atmosphere. The specific resistance of the obtained copper thin film is shown in Table 1.

Comparative Example 8
Table 1 shows the specific resistance of the copper thin film obtained in the same manner as in Comparative Example 7 except that the firing time was 1 hour instead of 10 minutes.

  Table 1 shows that in a conductive copper paste using hydrolyzable gelatin as a protective agent, a copper thin film having a low resistance can be obtained at a lower temperature or in a shorter time when firing with superheated steam. On the other hand, in the case of the conductive copper paste using polyvinylpyrrolidone as a protective agent, it can be seen that the specific resistance is high under the same firing conditions. Further, the specific resistance of the copper thin film is higher under the hydrogen-nitrogen mixed gas or under the nitrogen gas other than the superheated steam treatment as compared with the superheated steam treatment.

  A metal thin film having a low specific resistance can be obtained by subjecting the coating film obtained from the conductive paste of the present invention to a superheated steam treatment. The metal thin film thus obtained is also useful as a metal thin film forming material such as a metal / resin laminate, an electromagnetic shielding metal thin film, a conductive layer for plating, a metal wiring material, a conductive material, etc. It can be applied to antennas, electromagnetic wave shields, electrodes and the like.

Claims (6)

  A conductive paste for superheated steam treatment, comprising metal nanoparticles protected with a hydrolyzable protective agent.   The conductive paste according to claim 1, wherein the hydrolyzable protective agent is a protein.   3. The conductive paste according to claim 1, wherein the metal nanoparticles contain particles made of at least one of copper, copper oxide, and copper complex.   The conductive paste according to claim 1, wherein a heat treatment temperature in the superheated steam treatment is 200 ° C. or higher.   The manufacturing method of a metal thin film which forms a coating film using the electrically conductive paste in any one of Claims 1-4, and then heat-processes with a superheated steam to this coating film, and obtains a metal thin film.   The metal thin film manufactured by the manufacturing method of Claim 5.