JP2015056214A - Metal thin film production method and metal thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a metal thin film having low resistivity excellent in conductivity by using a metal fine particle dispersion by overheat steam treatment, and to provide a printed circuit board produced by the method.SOLUTION: Provided is a method for producing a metal thin film including a process in which a coating film including a metal fine particle dispersion is formed and then the coating film is subjected to heating treatment by overheat steam while subjected to compression treatment.

Description

  The present invention relates to a method for producing a low resistivity metal thin film excellent in conductivity from a metal fine particle dispersion, and a metal thin film produced by this method.

 Formation of a conductive layer or a conductive pattern by printing is performed by applying a conductive paste using conductive particles to screen printing or letterpress printing. In screen printing, flaky metal particles having a particle size of several μm or more are used as the conductive particles to be used, and the thickness of the circuit is 10 μm or more to ensure conductivity. In recent years, the density of conductive circuits has been rapidly increasing. In order to enable the formation of higher density circuits, finer metal fine particles have been developed.

 As the metal as the conductive particles, silver, copper, or nickel is generally used. Silver is not only expensive, but also has poor migration resistance, and it can become a serious defect depending on the application, while the demand for miniaturization of the circuit is increased. Nickel has poor conductivity. Copper is easily oxidized and the resulting oxide has poor conductivity. The conductivity deteriorates due to the heat treatment at the time of copper paste production or storage or at the time of copper thin film formation from the copper paste, or the oxide layer formed on the copper surface at the time of copper thin film storage. Furthermore, the negative effects of copper oxidation also occur when a cover film is laminated to the copper paste circuit to prevent oxidation and insulation. The formation and progress of the oxide layer on the copper surface may cause distortion between the cover film adhesive and the copper thin layer, resulting in a decrease in adhesion. Strain is also generated between the copper paste layer and the base material. This decrease in adhesion often occurs when stored at a temperature of 150 ° C. or higher for a long period of time.

 In order to prevent harmful effects caused by oxidation of copper particles, various studies have been made on copper paste. Patent Document 1 discloses a conductive paint containing metal copper powder, a resol type phenol resin, an amino compound, an amino group-containing coupling agent, and a 1,2-N-acyl-N-methyleneethylenediamine compound having a specific blending ratio. It is said that the amino compound functions as a conductivity improver and also as a reducing agent, preventing oxidation of the metal copper powder and contributing to maintaining the conductivity. Moreover, in patent document 1, when the particle size of metal copper powder is less than 1 micrometer, it is easy to be oxidized, and since the electroconductivity of the coating film obtained falls, it is considered unpreferable. On the other hand, it has been attempted to coat the surface of the copper powder with silver and use it as a conductive filler for a conductive paste. For example, in Patent Document 2, copper powder is dispersed in a chelating agent solution, a silver ion solution, A conductive paste is disclosed in which a reducing agent is sequentially added to deposit a silver film on the surface of copper powder and this is used as a conductive filler.

 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. For example, Patent Document 3 discloses a method of preparing a metal thin film by preparing a metal paste dispersed in an organic solvent containing copper fine particles having a particle size of 1000 mm or less and a specific component, and firing the metal paste coating film at 500 ° C. Is disclosed, and electrical wiring can be formed by this method. However, the metal paste disclosed in Patent Document 3 is formed of only volatile components except for copper powder, and the adhesion to the base material after firing is weak. Also, since the firing temperature is high, the choice of base material is greatly limited. Patent Document 4 discloses a method of making an ultrafine copper powder having a particle size of 0.1 μm or less from copper hydroxide and a reducing agent using ultrasonic waves. In Example of Patent Document 4, an electron microscope is used. Only the average particle size and shape of the copper ultrafine powder were confirmed, and it was not disclosed whether it was actually useful as a conductive filler for conductive paste. Since there is no description about suppressing the formation of an oxide film of copper ultrafine powder, it is presumed that a copper oxide film was formed on the surface of the copper ultrafine powder and was not useful as a conductive filler.

 Fine particles typified by nanoparticles are very easy to aggregate and difficult to disperse because of their very large surface area. The dispersibility of the metal fine particles can be improved by adsorbing the binder resin or dispersant to the metal fine particles, preventing the aggregation of the fine particles, improving the storage stability, and ensuring the fluidity of the dispersion. I can expect. However, as the metal fine particles become finer, a larger amount of binder resin or dispersant is required, and the binder resin or dispersant tends to prevent the metal fine particles from contacting each other and hinder the improvement in conductivity. In such a case, it may be necessary to remove the binder resin or the dispersant by sublimation or decomposition evaporation. In addition, the adhesion to a substrate such as a film or glass is likely to deteriorate due to firing. In addition to the problems peculiar to these metal particles, problems caused by oxidation are added to copper particles. The deterioration of conductivity due to oxidation of copper particles becomes more prominent as the particle diameter becomes smaller.

A method for treating a conductive paste coating film containing copper-based particles in a reducing atmosphere is disclosed. For example, in the macro wave surface wave plasma treatment (Patent Document 5), the thickness of the coat that can be treated is limited to 2 μm or less. Further, formic acid gas treatment (Patent Document 6) can be performed at a low temperature of 200 ° C. or lower, but there are concerns about the toxicity of formic acid 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 7) Although this method has the advantage of being able to process at room temperature in a short time, there is a problem that the irradiation apparatus is expensive and the conditions under which the substrate is not damaged are narrow.

  Furthermore, a method of applying pressure during heating and baking is disclosed. For example, Patent Documents 8 and 9 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 10 discloses a method of obtaining a copper film by arranging a shielding object immediately above a coating film containing copper particles and performing a 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 11, 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. In addition, it is recommended that heat and pressure treatment be performed before the superheated steam treatment. However, there is a problem that the effect of the heat and pressure treatment is relatively small.

JP-A-11-293185 JP-A-1-119602 Japanese Patent No. 2561537 JP 2005-23417 A Japanese Patent No. 5131191 International Publication No. 2011/034016 International Publication No. 2006/071419 JP 2005-177710 A JP 2008-124446 A JP 2010-146734 A Japanese Patent No. 485590

  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 method for producing a low resistivity metal thin film having excellent conductivity from a metal fine particle dispersion by superheated steam treatment, and a metal thin film produced by this method.

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, this invention consists of the following structures.
(1) A method for producing a metal thin film, comprising a step of forming a coating film containing a metal fine particle dispersion and subjecting the coating film to a heat treatment with superheated steam while performing a pressure treatment.
(2) The production according to (1), wherein the metal fine particles contained in the metal fine particle dispersion contain at least one selected from the group consisting of copper, copper oxides, and copper complexes. Method.
(3) The manufacturing method according to any one of (1) to (2), wherein the heat treatment temperature with superheated steam is 200 ° C. or higher.
(4) The metal thin film manufactured by the method containing the manufacturing method in any one of (1)-(3).

In the present invention, when a metal thin film is produced from a metal fine particle dispersion by performing a superheated steam treatment, a metal thin film having extremely excellent conductivity can be obtained by including a step of applying a pressure treatment.

Hereinafter, the present invention will be described in detail.
The present invention is characterized in that a metal thin film is produced by forming a coating film containing a metal fine particle dispersion and including a step of applying a pressure treatment during a heat treatment at 200 ° C. or higher with superheated steam. And The inventors of the present invention have found that a metal thin film having excellent conductivity can be obtained by performing a pressure treatment at the same time that a coating film containing a metal fine particle dispersion is heated with superheated steam, and the present invention is completed. It came to. The coating film is preferably one obtained by applying or printing a metal fine particle dispersion on an insulating substrate.

  In the present invention, when the heat treatment is performed with superheated steam, the treatment atmosphere becomes an oxygen-free or low-oxygen state, and even metal fine particles that are likely to be oxidized in the air, such as copper fine particles, are oxidized in the heat treatment step. Can be suppressed. As a result, the deterioration of conductivity due to oxidation hardly occurs. Furthermore, depending on the type of metal and the processing conditions, the oxide layer on the surface of the fine particles may be reduced, and the conductivity may be improved. In addition, when the coating film is formed by applying or printing a metal fine particle dispersion, the superheated steam is used to promote desorption of organic substances adsorbed on the metal fine particles, and as a result, the opportunity for contact between the metal fine particles May be increased, and the conductivity is further improved. In addition, since superheated steam has higher heating efficiency than heated air or heated nitrogen gas, firing may occur in a short time and / or at a low temperature.

  In the present invention, a metal thin film is produced by subjecting a coating film containing a metal fine particle dispersion to a heat treatment with superheated steam. The coating film is preferably one obtained by applying or printing a metal fine particle dispersion on an insulating substrate.

  The metal fine particle dispersion of the present invention is obtained by dispersing metal fine particles as a dispersoid in a dispersion medium, and may contain a binder resin capable of adsorbing the metal fine particles as necessary.

  The average particle size of the metal fine particles used in the present invention is preferably 2 μm or less, more preferably 0.5 μm or less, still more preferably 0.1 μm or less, and particularly preferably 0.08 μm 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.

  When the average particle size of the metal fine particles is larger than 2 μm, the metal fine particles are precipitated in the dispersion, or the printability of the fine circuit is deteriorated. Although the minimum of an average particle diameter is not specifically limited, It is preferable that it is 0.01 micrometer or more. If it is less than 0.01 μm, it may be difficult to obtain a highly conductive metal thin film because a large amount of a dispersion medium is required in order to limit the economical efficiency of metal fine particles and to obtain a stable dispersion. The metal fine particles used in the present invention may be used by mixing those having different particle diameters.

  As the metal fine particles used in the present invention, either fine particles fused by heat treatment or those not fused can be used. Examples of the metal include copper, nickel, cobalt, silver, platinum, gold, molybdenum, and titanium. Copper is particularly preferable, and is selected from the group consisting of copper fine particles, copper oxide fine particles, and copper complex fine particles. Particles containing at least one kind are preferred. These metal fine particles may be a commercially available product or can be prepared using a known method. In addition, a structure in which different kinds of metals are stacked, or an organic or inorganic material plated with metal may be used.

  The metal fine particle dispersion used in the present invention may 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 metal fine particle dispersion used in the present invention is preferably composed of metal fine particles, a solvent, and a binder resin. The proportion of each component is preferably in the range of 20 to 400 parts by weight of solvent and 3 to 15 parts by weight of binder resin with respect to 100 parts by weight of metal fine particles. The range of 20-50 weight part of solvent and 4-10 weight part of binder resin is more preferable.

  The solvent used in the metal fine particle dispersion used in the present invention is selected from those that dissolve the resin when a binder resin that functions to stabilize the dispersion is used. There may be. The dispersion medium has a role of adjusting the viscosity of the dispersion in addition to the role of dispersing the metal fine particles in the dispersion. Examples of the organic solvent suitably used as the solvent include alcohol, ether, ketone, ester, aromatic hydrocarbon, amide and the like.

  Examples of the binder resin used in the metal fine particle dispersion used in the present invention include polyester, polyurethane, polycarbonate, polyether, polyamide, polyamideimide, polyimide, and acrylic. A resin having an ester bond, a urethane bond, an amide bond, an ether bond, an imide bond or the like is preferable from the viewpoint of the stability of the metal fine particle dispersion.

  The fine metal particle dispersion used in the present invention preferably contains a polymer containing a functional group capable of adsorbing to a metal such as a sulfonate group or a carboxylate group. Furthermore, you may mix | blend a dispersing agent. Examples of the dispersant include higher fatty acids such as stearic acid, oleic acid, and myristic acid, fatty acid amides, fatty acid metal salts, phosphoric acid esters, and sulfonic acid esters. The amount of the dispersant used is preferably in the range of 0.1 to 10% by weight of the binder resin, and the effect of improving the dispersibility of the metal fine particles and the storage stability of the dispersion may be exhibited.

  A curing agent may be blended in the metal fine particle dispersion used in the present invention, if necessary. Examples of the curing agent that can be used in 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.

  As a method for obtaining the metal fine particle dispersion, a general method for dispersing powder in a liquid can be used. For example, after mixing a mixture of metal fine particles and a binder resin solution and, if necessary, an additional solvent, dispersion may be performed by an ultrasonic method, a mixer method, a three-roll method, a ball mill method, or the like. Of these dispersing means, a plurality of dispersing means can be combined for dispersion. These dispersion treatments may be performed at room temperature, or may be performed by heating in order to reduce the viscosity of the dispersion. If necessary, the reducing agent to be used may be added at any stage before, during or after the dispersion of the fine metal particle dispersion.

  In order to form a coating film containing the metal fine particle dispersion, a general method used when the dispersion is applied or printed on an insulating substrate can be used. For example, the metal fine particle dispersion 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, and then air-dried. The coating film can be formed by evaporating at least a part of the dispersion medium by heating or decompression. 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 copper 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 copper thin film that can be formed varies depending on the dispersion composition and the method of coating 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. is there. In order to obtain a thick copper 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.

  In forming the copper 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 copper thin film, or a copper thin film 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 copper thin film of the present invention, such as an insulating layer.

  In the present invention, the coating film formed from the metal fine particle dispersion is preferably subjected to a heating treatment with superheated steam after a drying treatment. A preferable drying temperature is 60 to 120 ° C., and a drying time is 3 to 20 minutes. When the superheated steam treatment is performed without a drying treatment step after coating, bumping may occur and the uniformity of the coating film may be deteriorated. 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.

  The metal thin film of the present invention can be obtained by subjecting the coating film containing the metal fine particle dispersion to a heat treatment with superheated steam. Superheated steam refers to steam that has been heated by heating saturated steam without increasing the pressure. Superheated steam can heat a substance in a short time because the radiant heat energy becomes remarkably larger than that of ordinary heated air at a temperature of 150 ° C. or higher.

  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 superheated steam treatment is preferably performed as a baking treatment of the coating film containing the metal fine particle dispersion. The firing treatment tends to exhibit a particularly high effect when the particle size of the metal fine particles is 100 nm or less. Although it varies depending on the surface state such as crystallinity and oxidation degree of the metal fine particles, so-called nanoparticles have a large surface activity and start to be fused at a temperature much lower than the generally known melting point of the bulk. In the present invention, the firing treatment refers to a heat treatment in which at least a part of the metal fine particles is fused, and it is not necessarily required to decompose or volatilize the binder resin and the dispersant.

  The temperature of the superheated steam used in the present invention is preferably 200 ° C. or higher, particularly preferably 250 ° C. or higher, and the specific resistance of the formed metal thin film tends to decrease with increasing temperature. 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 heat resistant resin layer 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 conductive layer having a low specific resistance cannot be obtained. If the temperature of the superheated steam is too high, most or all of the binder resin is removed, the adhesion between the metal thin film and the substrate may be impaired, and the heat-resistant resin layer may be deteriorated. It is.

  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. Depending on the type of metal, the reduction of the surface activity due to the formation of fine particles may cause a reduction reaction, and the conductivity may be dramatically improved. In particular, in the case of copper fine particles, a remarkable improvement in conductivity is recognized, and it is considered that reduction of the oxide layer formed on the surface of the copper fine particles occurs. The effect of improving the conductivity considered to be due to this reduction tends to increase as the particle diameter decreases. In the case of metal fine particles, such as copper fine particles, where the oxide film is easily formed, the conductive portion and the insulating portion can be patterned on the same surface by patterning the portion to be treated with superheated steam and the portion not to be treated. .

  In the present invention, by subjecting the metal coating to pressure treatment in all or part of the superheated steam treatment, there are fewer voids between the sintered metal particles in the coating, resulting in lower specific resistance. An excellent conductive metal thin film having a value can be obtained. The pressurizing method is not particularly limited as long as the coating film can be stably pressed and the metal particles can be sintered more densely. Examples of the pressing method include a pressing method using hydrostatic pressure and a roll pressing method. Further, a pressurizing method with other energy such as an ultrasonic press may be used. Among these, the roll pressurization method which can be manufactured by the roll-to-roll method is preferable. Conventionally, a high temperature double belt press machine is commercially available as a method of pressurizing at a high temperature. For example, a special high temperature double belt press machine (heating temperature to 400 ° C., applied pressure to 10 MPa, manufactured by Mitsubishi Chemical Engineering Co., Ltd.) can be mentioned. This device presses the work piece between the upper and lower metallic endless belts against the belt at high temperature and high pressure by induction heating rolls, as a substrate (copper foil + special film + copper foil) Widely adopted.

As a preferred method of the present invention, both ends of a heating furnace with superheated steam are partitioned with an air shower, an insulating base film having a metal thin film coating is supplied roll-to-roll to the entrance of the heat treatment furnace and wound from the outlet, and A method of using a device in which a press part (consisting of a metal endless double belt and an induction heating roll) of a high temperature double belt press machine is installed in a part of the heating furnace can be mentioned. In this way, pressure treatment can be performed during heating with superheated steam. The metal endless double belt is made of a stainless steel plate having a thickness of 0.6 to 3 mm, and the induction heating roll is preferably made hard by plating the surface of the base metal with hard chrome.
The applied pressure is preferably 0.1 MPa or more. If it is less than 0.1 MPa, the effect of the pressure treatment is small. The pressure is preferably 1 MPa or more, particularly preferably 5 MPa or more. That is, in the pressure treatment in the present invention, it is preferable to apply a high pressure within a range that does not damage the insulating substrate and the sintered metal thin film.

  In the present invention, when the metal thin film is a copper thin film, a rust prevention treatment can be performed. 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 treatment agent) that can form an adsorption layer on the surface of the metal thin film layer, preferably the copper thin film layer in the present invention, include benzotriazole, tolyltriazole, and tetrazole. Nitrogen heterocyclic compounds, sulfur-containing compounds such as mercaptopropionic acid, mercaptoacetic acid, thiophenol and triazinedithiol, amino compounds such as octylamine and isobutylamine, silane coupling agents, titanium coupling agents, chromate treatment agents, etc. . 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.

  Examples of the waterproof insulating resin provided on the metal thin film layer, preferably the copper thin film layer in the present invention 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 rust prevention 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 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 Method of Electric Resistance The electric 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. Evaluation method of adhesion Using 1cm width of cello tape (registered trademark) “CT405AP-15” manufactured by Nichiban Co., Ltd., and sticking 5cm length of the adhesive tape on the metal thin film surface, the metal thin film surface is damaged when peeled off It was judged by visual observation whether it received or not. When some damage such as peeling, floating and cracking was observed on the metal thin film, it was judged as x, and when no damage was found, it was judged as ○.

The heat treatment and pressurization treatment with superheated steam in the examples were performed by the following method.
As a superheated steam generator, a steam superheater (“DHF Super-Hi 10” manufactured by Daiichi RF Co., Ltd.) was used, and a heat treatment furnace for supplying the generated superheated steam from a number of nozzles was used. Both ends of the heating furnace are separated by an air shower, and a pressurizing roll that can be heated (part of the double belt press machine for high temperature (consisting of a double belt and nine induction heating rolls) is installed in the heat treatment furnace. An insulating base film having a metal thin film coating was supplied roll-to-roll to the entrance of the heat treatment furnace and wound up from the exit.The heat treatment time was the residence time in the heat treatment furnace. The pressurizing treatment was carried out at a predetermined temperature with the press unit in a nitrogen gas atmosphere without using superheated steam in the above apparatus.

Synthesis example (synthesis of binder resin)
A composition having the following blending ratio was put into a four-necked flask equipped with a stirrer and stirred and heated to obtain a copolymerized polyester according to a conventional method.
80 parts of cis-1,2-cyclohexanedicarboxylic anhydride (HHPA)
1,4-cyclohexanedicarboxylic acid (CHDA) 20 parts
The number average molecular weight of 100 parts of the copolymer polyester obtained by 100 parts of 2-methylpropanediol was 32461, and the glass transition temperature was 11 ° C.

Example 1
The following proportion of the composition was dispersed with a three roll mill. Furthermore, it diluted with the solvent and apply | coated so that the thickness after drying might be set to 5 micrometers, and it dried with hot air at 120 degreeC for 2 minutes, and obtained the copper thin film laminated body.
(Composition)
Co-polyester n-butyl carbitol acetate 35% by weight solution 1.8 parts copper fine particles (RCA-16, average particle size 0.8 μm, DOWA Electronics Co., Ltd.) 20 parts ethyl carbitol acetate 3 parts

  Subsequently, the copper thin film laminate was baked with superheated steam at 300 ° C. for 10 minutes with the superheated steam heat treatment pressure apparatus. The pressure of the roll pressurization process at that time was 5 MPa. About the obtained copper thin film laminated body, specific resistance and adhesiveness were measured and the value was shown in Table 1. The specific resistance of the copper thin film was sufficiently low and the adhesion was good.

Examples 2-3
A copper thin film was obtained in the same manner as in Example 1 except that the pressure in the roll pressurizing treatment was 1 MPa (Example 2) and 10 MPa (Example 3) instead of 5 MPa. Specific resistance and adhesion are shown in Table 1. The specific resistance of the copper thin film was sufficiently low and the adhesion was good.

Examples 4-6
A copper thin film was obtained in the same manner as in Example 1 except that the firing temperature was 200 ° C. (Example 4), 250 ° C. (Example 5), and 350 ° C. (Example 6) instead of 300 ° C. Specific resistance and adhesion are shown in Table 1.

Comparative Example 1
A copper thin film was obtained in the same manner as in Example 1 except that the roll pressure treatment was not performed. Specific resistance and adhesion are shown in Table 1. It can be seen that the specific resistance of the copper thin film is higher than that of Example 1.

Comparative Examples 2-4
A copper thin film was obtained in the same manner as in Comparative Example 1 except that the firing temperature was 150 ° C. (Comparative Example 2), 200 ° C. (Comparative Example 3), and 350 ° C. (Comparative Example 4) instead of 300 ° C. Specific resistance and adhesion are shown in Table 1. It can be seen that the specific resistance of the copper thin film is high compared to the case where the pressure treatment is performed.

Comparative Example 5
The copper thin film laminate obtained by applying and drying with hot air at 120 ° C. for 2 minutes as described in Example 1 was subjected to a pressure treatment of 5 MPa at room temperature, and then not subjected to the pressure treatment as in Comparative Example 1, A baking process with superheated steam at 300 ° C. for 10 minutes was performed to obtain a copper thin film. Specific resistance and adhesion are shown in Table 1. Compared with Example 1, it turns out that the pressurization process of the normal temperature before a superheated steam process has no effect regarding the specific resistance of a copper thin film compared with a superheated steam process.

Comparative Examples 6-7
The copper thin film obtained in Comparative Example 1 was subjected to pressure treatment (in nitrogen) at room temperature (Comparative Example 6) or 100 ° C. (Comparative Example 7) to obtain a copper thin film. Specific resistance and adhesion are shown in Table 1. Compared with Example 1, it turns out that the pressurization process at normal temperature or 100 degreeC has no effect regarding the specific resistance of a copper thin film after a superheated steam process.

  According to the present invention, a metal thin film having a low specific resistance on an insulating substrate can be obtained from a coating film containing a metal fine particle dispersion. It is also useful as metal thin film forming materials such as metal / resin laminates, electromagnetic shielding metal thin films, conductive layers for plating, metal wiring materials, conductive materials, etc., and is applied to conductive circuits, antennas, electromagnetic shielding bodies, electrodes, etc. be able to.

Claims (4)

  A method for producing a metal thin film, comprising: forming a coating film containing a metal fine particle dispersion, and performing a pressure treatment while subjecting the coating film to a heat treatment with superheated steam.   2. The production method according to claim 1, wherein the metal fine particles contained in the metal fine particle dispersion contains at least one selected from the group consisting of copper, copper oxides, and copper complexes.   The manufacturing method according to claim 1, wherein the heat treatment temperature with superheated steam is 200 ° C. or higher.   The metal thin film manufactured by the method containing the manufacturing method in any one of Claims 1-3.