JP2009259806A - Method of manufacturing porous copper sintered film, and porous copper sintered film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper particulate dispersed solution with high dispersibility and superior conductivity even after baking at a comparatively low temperature below 250°C after arrangement and drying on a substrate, and capable of providing a conductive member with little impurity, and to provide a method of forming a conductive circuit with high conductivity by a heating calcination method of applying a metal particulate dispersed liquid on a substrate. <P>SOLUTION: The method of manufacturing the porous copper sintered film is characterized in that a copper particulate dispersed solution L of dispersing copper particulates wherein a mean particle size of primary particles is 1-500 nm in a solvent S configured such that it becomes a concentration of 2-70 mass% is applied on the substrate, the copper particulates are sintered by inserting the substrate applied with the copper particulate dispersed solution L into a furnace heated to 160-500°C and quickly heating it in an inert gas atmosphere, and the sintered film with porosity of 40-70% is formed on the substrate. A porous copper sintered film being one example of the porous copper sintered film is indicated in the figure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for producing a porous copper sintered film, and a porous copper sintered film obtained by the production method and the like.
Low resistance transparent conductive films such as porous copper sintered films are used in flat panel displays (FPDs) such as liquid crystal displays (LCDs) and organic electroluminescence (OELs). ) Transparent conductive film.

A light-transmitting conductive material is used as an electrode of display elements such as a liquid crystal display element and an EL display element. As such a light-transmitting conductive material, indium oxide-tin oxide system (ITO), antimony oxide-tin oxide system (ATO), etc. are known, and vacuum deposition, sputtering, CVD (chemical vapor deposition; It is manufactured by being attached to a substrate such as glass by a chemical vapor deposition method, a dip coating method, a spray method, a spin coating method, or the like.
When an ITO transparent conductive film is produced by a dip coating method, a solution obtained by dissolving a metal organic acid salt in an organic solvent is widely used as a coating solution for a substrate. In addition, as a method of forming an indium oxide film by dip coating, a method of using about 5 mol% of tin chloride added to indium chloride and dissolving it in an aqueous solution or the like is also known, but it is formed when indium chloride is used. The film may become cloudy. In order to prevent the white turbidity, a method of forming an indium fluoride-based film by adding hydrofluoric acid to a spray solution (Patent Document 1), or a method using indium nitrate as an inorganic salt (Patent Document 2, Patent Document 3). ) Is disclosed.

  In the above Patent Document 3, an organic tin compound other than stannic chloride is used in order to improve the conductivity of the film. Further, Patent Document 4 below discloses a method of adding an organic aminosilane ester to a solution containing an inorganic salt of indium. However, in this method, a large amount of silicon contained in the raw material aminosilane ester is finally obtained as silicon dioxide. The volume resistivity becomes a very large value.

JP 51-75991 A JP-A-55-51737 JP-A 63-9018 JP-A-6-96687

The coating methods such as the dip coating method and the spin coating method can provide a high-quality transparent conductive film with high smoothness and can cope with a large area. When forming an indium oxide film by these methods, indium nitrate, which is mainly used as a raw material for forming it, has the advantage of being difficult to evaporate, but has a problem that excellent conductivity cannot be obtained because of its high thermal decomposition temperature. There is. For example, in the method using indium nitrate as a raw material described in Patent Document 2, it is disclosed that a film having a minimum coating thickness of 40 nm is applied several times to reduce the resistance. The resistivity is as large as about 4.5 × 10 ⁻² Ω · cm. Therefore, a reduction in resistance of the ITO film is required. For this purpose, it is necessary to increase the sintering temperature and the film thickness. However, raising the firing temperature limits the choice of substrate, while increasing the film thickness has the problem of loss of transparency. In addition, the transparent conductive film is mainly made of an ITO film using indium with less resources, and there is a problem of resource depletion.

In the material used for the conventional transparent conductive film, the electrical resistance (sheet resistance) after sintering is as high as several kΩ / □ at low temperature heating, and if it is attempted to obtain a material with low electrical resistance, Since high temperature heating (for example, about 300 ° C. or higher) is required, there is a problem that it cannot be used for forming a transparent conductive film in the field of flat panel displays such as LCD and organic EL. Therefore, a transparent conductive film that can be sintered at a low temperature and has a low resistance value and a method for producing the same are demanded.
An object of the present invention is a thin film-like transparent conductive material capable of lowering the sintering temperature without using an ITO film made of indium, and having a small electric resistance (sheet resistance) after sintering. It is in providing the manufacturing method of a film | membrane, and the obtained low resistance transparent conductive film.

In view of the above circumstances, the present inventors have sintered a nano-size (1 μm or less) copper fine particle dispersion solution by heat treatment under various conditions. As a result, the base material is a dispersion solution in which copper fine particles are dispersed. After the coating, a method for producing a porous copper thin film having low electrical resistance and high light transmittance by rapid heating was found, and the present invention was completed.
That is, the gist of the present invention is the invention described in the following (1) to (17).
(1) A copper fine particle dispersion solution (L) dispersed in a solvent (S) so that copper fine particles having an average primary particle size of 1 to 500 nm have a concentration of 2 to 70% by mass is applied to a substrate. Next, the base material coated with the copper fine particle dispersion (L) is inserted into a furnace in an inert gas atmosphere heated to 160 to 500 ° C. and rapidly heated to sinter the copper fine particles. A method for producing a porous sintered copper film (hereinafter sometimes referred to as a first embodiment), wherein a sintered film having a porosity of 40 to 70% is formed on a substrate.
(2) The substrate coated with the copper fine particle dispersion (L) is housed in a container under an inert gas atmosphere and inserted into the heated furnace (1) The manufacturing method of the porous copper sintered film as described in 1).
(3) The method for producing a porous sintered copper film according to (2), wherein the inert gas is nitrogen gas or argon gas, and the container is a glass container.
(4) The method for producing a porous sintered copper film according to any one of (1) to (3), wherein the thickness of the coating solution on the substrate is in the range of 1 μm to 3 mm.
(5) The porous structure according to any one of (1) to (4), wherein the porous copper sintered film has a light transmittance of 30% or more in the film thickness direction of light having a wavelength of 460 nm. Of manufacturing a sintered copper film.
(6) The porous copper sintered film according to any one of (1) to (5), wherein the sheet resistance value of the porous copper sintered film is 0.01 to 5Ω / □. Method.
(7) At least a part of the surface of the copper fine particle dispersion (L) is covered with a dispersant (including a polymer compound) selected from a compound consisting of carbon, hydrogen, oxygen, and nitrogen atoms. The porous copper according to any one of (1) to (5), wherein the porous copper is dispersed in a dispersion solvent (including a mixed solvent) (S) having a boiling point of 60 ° C. or higher and 400 ° C. or lower. A method for producing a sintered film.
(8) The dispersion solvent (S) has an organic solvent (S1) composed of an alcohol (A) having 1 and / or 2 or more hydroxyl groups in the molecule, or 1 and / or 2 or more hydroxyl groups in the molecule. Any one of the above (1) to (7), which is a mixed solvent (S2) containing 20 to 40% by volume of alcohol (A) and 60 to 80% by volume of an organic solvent (B) having an amide group. A method for producing a porous sintered copper film.
(9) The organic solvent (A) is ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-butene-1,4-diol, 2,3-butanediol, pentanediol, hexanediol, octanediol, glycerol, 1,1,1-trishydroxymethylethane, 2-ethyl-2-hydroxymethyl-1, Selected from 3-propanediol, 1,2,6-hexanetriol, 1,2,3-hexanetriol, 1,2,4-butanetriol, threitol, erythritol, pentaerythritol, pentitol, and hexitol The porous copper sintered film according to (8), which is one or more types Manufacturing method.
(10) The organic solvent (B) is N-methylacetamide, N-methylformamide, N-methylpropanamide, formamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N, N -Described in (8) above, which is one or more selected from dimethylformamide, 1-methyl-2-pyrrolidone, hexamethylphosphoric triamide, 2-pyrrolidinone, ε-caprolactam, and acetamide. Manufacturing method of porous copper sintered film.

(11) The light transmittance in the film thickness direction of light having a porosity of 40 to 70% and a wavelength of 460 nm obtained by sintering copper fine particles having an average primary particle diameter of 1 to 500 nm is 30%. A porous copper sintered film having a sheet resistance value of 0.01 to 5Ω / □ as described above (hereinafter sometimes referred to as a second embodiment).
(12) After applying a copper fine particle dispersion (L) in which copper fine particles having an average primary particle diameter of 1 to 500 nm are dispersed on a substrate, the inert particles are heated in a furnace heated to 160 to 500 ° C. The porous copper sintered film according to (11), which is obtained by sintering in a gas atmosphere.
(13) Porous copper firing as described in (11) or (12) above, wherein the transmittance in the film thickness direction of light having a wavelength of 460 nm is 50% or more and the sheet resistance value is 0.01 to 5Ω / □. conjunctiva.
(14) The porous copper sintered film according to any one of (11) to (13), wherein a density of the sintered film is in a range of 1.5 to 5.5 g / cm ³ .
(15) The porous copper sintered film according to any one of (11) to (14), wherein the sintered film has a thickness in a range of 50 nm to 10 μm.
(16) The porous copper sintered film according to any one of (11) to (15), which is used for a transparent conductive film for a flat panel display (FPD).
(17) The porous copper sintered film according to any one of (11) to (16), wherein the sintered film is formed of a mixture of copper fine particles and transparent particles.

According to the method for producing a porous copper sintered film of the present invention, it is possible to produce a porous copper sintered film having extremely high porosity from nanoparticles. The porous copper sintered film of the present invention is a sintered film having a much higher porosity than the known porous copper sintered film and excellent in light transmission and conductivity, and is used for flat panel displays such as LCD and organic EL. It can be used as a light transmissive conductive film in the field.
Further, copper has a lower reflectance of white light (near 460 nm) in the visible light region (wavelength of about 380 to 750 nm) than silver, and can transmit light more efficiently.

A scanning electron microscope (SEM) photograph of the porous copper sintered film obtained in Example 3, which is an example of the porous copper sintered film of the present invention, is shown in FIG. 1 as a perspective view. FIG. 2 shows a scanning electron microscope (SEM) photograph of the porous copper sintered film obtained in Comparative Example 1, which is an example of a conventional porous copper sintered film, as a perspective view. A scanning electron microscope (SEM) photograph of the porous copper sintered film obtained in Example 6, which is an example of the porous copper sintered film of the present invention, is shown in FIG. 3 as a perspective view. FIG. 4 shows a conceptual diagram of the porous copper sintered film obtained in Example 8, which is an example of the porous copper sintered film of the present invention.

[1] About “Method for Producing Porous Copper Sintered Membrane” as First Aspect “The method for producing porous copper sintered membrane”, which is the first embodiment, has an average primary particle diameter of 1 to 500 nm. The copper fine particle dispersion solution (L) dispersed in the solvent (S) so that the concentration of copper fine particles was 2 to 70% by mass was applied to the substrate, and then the copper fine particle dispersion solution (L) was applied. The base material is inserted into a furnace in an inert gas atmosphere heated to 160 to 500 ° C. and rapidly heated to sinter the copper fine particles, and a sintered film having a porosity of 40 to 70% is used as the base material. It is formed on the top.
Hereinafter, the manufacturing method of the porous copper sintered film of this invention is demonstrated.

(1) Copper fine particle dispersion (L)
(I) Production of copper fine particles The method for producing copper fine particles is not particularly limited. However, as long as fine particles (P) having an average primary particle diameter of 1 to 500 nm can be formed, both electrolytic reduction and electroless reduction can be performed. Can be adopted,
As the electrolytic reduction and electroless reduction methods, known methods can be adopted. In this case, the copper ions are dispersed in the aqueous solution as copper fine particles which are liquid phase reduced and covered with the dispersant (D).
Usable copper ions include copper hydroxide, copper nitrate, nitrite, copper acetate, copper formate, ammonium salt, copper citrate, copper oxalate, copper gluconate, nitric acid that form monovalent or divalent copper ions It is preferable to use one or more selected from copper, copper formate, copper benzoate, copper tartrate, copper oxide, copper oleate, and acetylacetone copper, and practically a monohydrate of copper (II) acetate ( The use of (CH ₃ COO) ₂ Cu · 1H ₂ O) is particularly desirable. A preferable copper ion concentration in the reduction reaction solution is 0.01 to 4.0 mol / liter. If the copper ion concentration is less than 0.01 mol / liter, the production amount of copper particles is reduced and the yield of copper fine particles from the reaction phase is lowered. There is a risk of coarse aggregation between particles. A more preferable copper ion concentration is 0.05 to 0.5 mol / liter.

In the case of electrolytic reduction, for example, by applying a potential between an anode and a cathode provided in an aqueous solution containing metal ions, copper fine particles whose surfaces are covered with a dispersant (D) described later are applied in the vicinity of the cathode. Can be formed. In electroless reduction, for example, a reducing agent is added to an aqueous solution containing a dispersant (D) and metal ions to perform a reduction reaction to form copper fine particles whose surface is covered with the dispersant (D). Can do.
Examples of the reducing agent include sodium borohydride, hydrazine, dimethylaminoborane, trimethylaminoborane and the like, and two or more of these can be used in combination. In addition, you may mix | blend hydrophilic solutions other than water with a liquid phase reducing aqueous solution as a reaction solvent.

(Ii) Average particle size of copper fine particles Control of the average particle size of the primary particles of the fine particles (P) can be achieved, for example, when the fine particles (P) are formed by a reduction reaction, D), adjustment of the type and concentration of the reducing agent, and adjustment of the stirring speed, temperature, time, pH and the like when the metal ions are reduced.
The copper fine particles obtained by the above electrolytic reduction have a particle diameter in the range of about 1 to 500 nm, and the shape thereof is a fine particle with little cohesiveness.
Here, the average particle diameter of primary particles means the diameter of primary particles of fine particles such as individual metals constituting secondary particles. The diameter of the primary particles can be measured using a transmission electron microscope (TEM). Moreover, an average particle diameter means the number average particle diameter of a primary particle.

(Iii) Dispersant (D)
In the present invention, a dispersant is used when forming copper fine particles by a reduction reaction.
The dispersant is soluble in water and is present so as to cover the surface of the copper fine particles deposited in the reaction system, thereby preventing the copper fine particles from aggregating and maintaining good dispersibility. Has an effect.
Although the addition amount of a dispersing agent is based also on the density | concentration of the copper fine particle produced | generated from reduction reaction aqueous solution, 0.1-500 weight part is preferable with respect to 100 weight part of this copper atom, and 5-100 weight part is more preferable. . When the added amount of the dispersant is less than 0.1, the effect of suppressing aggregation may not be sufficiently obtained. On the other hand, when the amount exceeds 500 parts by weight, the fine particle-dispersed aqueous solution may be used without any problem in dispersion. After coating, during drying and firing, an excessive dispersant may inhibit the sintering of the copper fine particles and reduce the denseness of the film quality, and the firing residue of the dispersant remains in the metal film. As a result, the conductivity may be reduced.
The dispersant of the present invention is not particularly limited as long as it has the above action and exhibits the above action in an aqueous solution.

As a dispersing agent, although depending on its chemical structure, it has a molecular weight of about 100 to 100,000, has good solubility in water, and well disperses copper fine particles precipitated by reduction reaction from copper ions in an aqueous solution. And a dispersant of a compound (including a polymer compound) composed of two or more atoms selected from a carbon atom, a hydrogen atom, an oxygen atom, and a nitrogen atom.
The dispersant is preferably an amine polymer such as polyvinylpyrrolidone or polyethyleneimine; a hydrocarbon polymer having a carboxylic acid group such as polyacrylic acid or carboxymethylcellulose; an acrylamide such as polyacrylamide; One or more selected from ethylene oxide, starch, and gelatin.
Specific examples of the dispersant compound exemplified above include polyvinylpyrrolidone (molecular weight: 1000 to 500,000), polyethyleneimine (molecular weight: 100 to 100,000), carboxymethylcellulose (to the carboxymethyl group of the hydroxyl group Na salt of alkali cellulose). Substitution degree: 0.4 or more, molecular weight: 1000 to 100,000, polyacrylamide (molecular weight: 100 to 6,000,000), polyvinyl alcohol (molecular weight: 1000 to 100,000), polyethylene glycol (molecular weight: 100) -50,000), polyethylene oxide (molecular weight: 50,000-900,000), gelatin (average molecular weight: 61,000-67,000), water-soluble starch and the like.

The liquid phase reduction is preferably reduction of copper ions by electrolytic reduction or electroless reduction using a reducing agent in an aqueous solution in which the dispersant (D) is dissolved. In addition, a well-known technique can be employ | adopted for the electroless reduction using the said electrolytic reduction or a reducing agent.
Here, “in the aqueous solution in which the dispersant (D) is dissolved” in the present invention may be that a metal ion and a reducing agent may be added to a reaction system in which the dispersant (D) is dissolved in advance. The dispersing agent (D), metal ion, and reducing agent may be dissolved in an aqueous solution in separate containers, and each may be added to another reaction container to perform a reduction reaction. Since the dispersant (D) in the present invention has the effect of improving the dispersion stability of the copper fine particles and improving the yield of copper fine particle production, it is present in the reaction system when or immediately after the copper fine particles are formed. Preferably it is.

(Iv) Recovery of copper fine particles After the completion of the above reduction reaction, an aggregation accelerator (F) is added to the aqueous reaction solution to reduce the dispersing action of the dispersant (D), and coarse particles are precipitated in the aqueous solution. Washed with water or an alcohol solution, etc., or recovered, or the coarse particles were precipitated in the aqueous solution and then washed with water or an alcohol solution if necessary, and the surface was covered with the dispersant (D). Copper fine particles can be obtained. Hereinafter, the above-described aggregation accelerator (F) will be described.

As such an aggregation accelerator (F), an oxidizing substance or a halogen compound can be used.
Examples of the oxidizing substance include oxygen gas, hydrogen peroxide, and nitric acid.
Examples of the halogen compound include methyl chloride, methylene chloride, chloroform, carbon tetrachloride, ethyl chloride, 1,1-dichloroethane, 1,2-dichloroethane, 1,1-dichloroethylene, 1,2-dichloroethylene, and trichloro. Ethylene, acetylene tetrachloride, ethylene chlorohydrin, 1,2-dichloropropane, allyl chloride, chloroprene, chlorobenzene, benzyl chloride, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, α- Examples thereof include one or more selected from chloronaphthalene, β-chloronaphthalene, bromoform, and bromobenzene. By using such an aggregation accelerator (F), copper fine particles can be efficiently separated and recovered from the aqueous reduction reaction solution.
The recovery operation is recovered by filtration through an operation such as centrifugation. When it is necessary to remove impurities, such as when a reducing agent is used in liquid phase reduction, the impurities are removed by washing with water or alcohol under conditions that do not completely remove the dispersant (D). Thus, copper fine particles whose surface is covered with the dispersant (D) can be obtained.

(V) Redispersion of copper fine particles The copper fine particle dispersion solution (L) (hereinafter sometimes referred to as “dispersion solution (L)”) has an average primary particle size of 1 to 1 obtained by the production method described above. Copper fine particles of 500 nm are dispersed in the dispersion solvent (S) to obtain a dispersion solution (L) having a concentration of 2 to 70% by mass.
When the copper fine particle concentration is less than 2% by mass, the mechanical strength of sintering by rapid heating is lowered. On the other hand, when it exceeds 70% by mass, it is difficult to obtain a porous copper thin film having a high porosity. There is a risk of becoming. The dispersion solvent (S) that can be used in the dispersion solution (L) preferably has a boiling point of 60 ° C. or higher. Further, the residual amount of impurities when the dispersion solution is applied on a substrate and then sintered is determined. (B) carbon atom, hydrogen atom and oxygen atom, (c) carbon atom, hydrogen atom and nitrogen atom, or (d) carbon atom, hydrogen atom, oxygen atom and It is preferable to use one type of compound consisting of nitrogen atoms or two or more types of solvents.
Accordingly, the dispersion solvent (S) is an organic solvent (S1) composed of an alcohol (A) having 1 and / or 2 or more hydroxyl groups in the molecule, or an alcohol having 1 and / or 2 or more hydroxyl groups in the molecule ( A) A mixed solvent (S2) containing 20 to 40% by volume and an organic solvent having an amide group (B) 60 to 80% by volume is more preferable.

The organic solvent (A) is ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2- Butene-1,4-diol, 2,3-butanediol, pentanediol, hexanediol, octanediol, glycerol, 1,1,1-trishydroxymethylethane, 2-ethyl-2-hydroxymethyl-1,3- 1 selected from propanediol, 1,2,6-hexanetriol, 1,2,3-hexanetriol, 1,2,4-butanetriol, threitol, erythritol, pentaerythritol, pentitol, and hexitol Species or two or more types can be exemplified.
The organic solvent (B) is N-methylacetamide, N-methylformamide, N-methylpropanamide, formamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N, N-dimethylformamide 1-methyl-2-pyrrolidone, hexamethylphosphoric triamide, 2-pyrrolidinone, ε-caprolactam, and acetamide can be exemplified.

(Vi) Improvement of dispersibility by stirring of the copper fine particle dispersion (L) In the dispersion solution (L) thus obtained, copper fine particles having an average primary particle diameter of 1 to 500 nm are at least partially on the surface. Although it is covered with a dispersing agent and dispersed in an aqueous solution in a state of low secondary aggregation, it is desirable to further improve the dispersibility by stirring. As a stirring method of the dispersion solution (L), a known stirring method can be employed, but it is preferable to employ an ultrasonic irradiation method.
The ultrasonic irradiation time is not particularly limited and can be arbitrarily selected. For example, if the ultrasonic irradiation time is arbitrarily set between 5 and 60 minutes, the average secondary aggregation size tends to be smaller as the irradiation time is longer. Further, when the ultrasonic wave irradiation time is lengthened, the dispersibility is further improved.
The dispersion solution (L) thus obtained is dispersed in the aqueous solution with the copper fine particles covered with the dispersant. The mechanism by which such a dispersing agent disperses copper fine particles is not completely elucidated, but for example, an atomic part having an unshared electron pair of a functional group present in the dispersing agent is adsorbed on the surface of the copper fine particles. It is expected that repulsive force is generated that forms a molecular layer and does not allow copper fine particles to approach each other.

(2) Application of copper fine particle dispersion solution (L) onto a base material (i) Base material For a base material that is a substrate to be coated with a copper fine particle dispersion solution (L), commonly used glass base materials and heat resistance Examples of the shape include flat plates, three-dimensional objects, and films. As the heat resistant synthetic resin, polyimide, epoxy resin, polycarbonate, fluororesin, or the like can be used. The substrate to be treated is preferably washed with pure water or ultrasonic waves before applying the dispersion solution (L).

(Ii) Application of copper fine particle dispersion solution (L) onto a substrate The dispersion solution (L) of the present invention is, for example, spin coating, spray coating, ink jet coating, dip coating, roll coating, screen printing, or dropping. It can apply | coat using well-known methods, such as a method.
The thickness of the coating film on the substrate varies depending on the concentration of the copper fine particles in the copper fine particle dispersion solution (L), the porosity, the thickness of the porous copper sintered film, etc., and cannot be determined in general. When forming a sintered film by rapid heating of the present invention, it is desirable that the thickness of the coating solution on the substrate is in the range of 1 μm to 3 mm in consideration of sinterability, porosity, mechanical strength, etc. . Further, from the viewpoint of light transmittance, it is more desirable to be in the range of 1 μm to 1 mm. Furthermore, it is more preferable that it is in the range of 1 μm to 300 μm.
Here, the rapid heating means, for example, that a base material coated with the dispersion solution (L) is inserted into a preheated furnace and the dispersion solvent (S) in the dispersion solution (L) is evaporated in a short time. A heating process in which copper fine particles are sintered together. That is, it refers to a heat treatment for evaporating the dispersion solvent (S) in a short time.

(3) Sintering of the copper fine particle dispersion (L) on the base material In the first aspect, the base material coated with the copper fine particle dispersion solution (L) is inserted into a furnace heated to 160 to 500 ° C. Then, the copper fine particles are sintered by rapid heating, and a sintered film having a porosity of 40 to 70% is formed on the substrate.
In general, when forming a conductive sintered film by sintering the copper fine particle dispersion (L), the solvent is first removed by heating the metal fine particle dispersion applied on the substrate in the drying step. Thereafter, the metal fine particles are sintered at a high temperature in the sintering step. In the present invention, the copper fine particle dispersion solution (L) is applied on the base material in a heated furnace without particularly providing a drying step. It is characterized by inserting a bowl and heating rapidly.
Thus, without providing a drying step, by inserting the copper fine particle dispersion solution (L) applied on the base material into a furnace heated to a temperature equal to or higher than the boiling point of the solvent (S), the solvent (S ) Causes boiling phenomenon, while sintering of the copper fine particles proceeds, and as a result, a porous copper sintered film having a high porosity is obtained.

(I) Sintering temperature and sintering time In this invention, although sintering temperature is the range of 160-500 degreeC, the heating temperature of a preferable furnace changes with boiling points of the solvent (S) to be used. Strictly speaking, it is also affected by the heat capacity of the solvent (S) and the heat capacity including the gas in the furnace, but since the amount of the solvent (S) is relatively small, the heat capacity is also small. The heating temperature condition is important.
Although the heating temperature of the furnace is in the range of 160 to 500 ° C., the vapor pressure of the solvent (S) is further 2 × (1.01325 × 10 ⁻¹ ) to 8 × (1.01325 × 10 ⁻¹ ) (MPa ) (Where 1.01325 × 10 ⁻¹ (MPa) is 1 atm), and the temperature at which the solvent (S) causes a boiling phenomenon is preferable. When the heating temperature is 150 ° C. or higher, the sintering of the copper fine particles proceeds, and the vapor pressure of the solvent (S) is 2 × (1.01325 × 10 ⁻¹ ) to 8 × (1.01325 × 10 ⁻¹ ). Since the solvent (S) is heated rapidly in the temperature range of (MPa) to cause a boiling phenomenon, it is presumed that the copper fine particles undergo partial sintering in a shape with a higher porosity. As the sintering temperature is higher, the light transmittance can be improved. On the other hand, since the mechanical strength is lowered, it is necessary to select a solvent (S) and a sintering temperature according to the purpose of use.

  The heating temperature of the furnace is such that the thicker the coating thickness of the copper fine particle dispersion solution (L) on the substrate, the longer the evaporation time of the solvent. Although it is desirable to set a high value, when copper fine particle dispersion (L) is applied on a substrate for electronic equipment to sinter the copper fine particles, or when used as a transparent conductive film for flat panel display (FPD) It is preferable to select a solvent (S) that enables sintering at 250 ° C. or lower. After sintering under the above heating conditions, the sintered zone is taken out of the furnace and cooled, but the heating time in the furnace is about 3 to 30 minutes. If it is less than 3 minutes, the sintering of the copper fine particles does not proceed sufficiently. On the other hand, the possibility that the sintering further proceeds even if heated for 30 minutes or more is low.

(Ii) Sintering under inert gas atmosphere In the present invention, the sintering of the copper fine particles from the copper fine particle dispersion solution (L) is not necessarily performed under a reducing gas atmosphere such as hydrogen gas, It can be performed in an inert gas atmosphere such as argon gas. In the present invention, since the copper fine particles are sintered by rapid heating in the furnace, in order to prevent the copper fine particles from undergoing an oxidation reaction due to oxygen in the atmosphere under a high temperature atmosphere, It is desirable that the substrate is placed in an inert atmosphere in advance before inserting the substrate coated with the copper fine particle dispersion (L). The means for making the atmosphere an inert gas atmosphere is not particularly limited, but a specific example is a heat-resistant glass container having a cylindrical outer shape with a lid on one side, and nitrogen gas is applied to the lid. A container having a supply port and a discharge port for nitrogen gas on the opposite surface of the lid can be used. A base material coated with the copper fine particle dispersion (L) is inserted into the container, a lid is attached, and the base is inserted into a furnace heated to a predetermined temperature under a nitrogen gas flow. The heat-resistant glass container is taken out from the substrate, cooled in the air, and when the sintered film on the substrate is cooled to room temperature, the flow of nitrogen gas is stopped and a porous copper sintered film is formed from the heat-resistant glass container. The formed base material can be taken out.

(Iii) Porous copper sintered film The porous copper sintered film obtained by the above sintering operation has a porosity of 40 to 70%, high visible light permeability, low sheet resistance, and mechanical strength. And it is excellent also in the adhesiveness to a base material.
FIG. 1 shows an example of a perspective view of a “porous copper sintered film” obtained by the “method for producing a porous copper sintered film” according to the first aspect of the present invention, taken with a scanning electron microscope (SEM) photograph. A photograph of a cross section perpendicular to the surface is shown in FIG. From these figures, it can be understood that the porous copper sintered film is continuously sintered three-dimensionally and opened to the outside of the sintered film, so that high light transmittance can be obtained. In order to obtain high light transmittance, a higher porosity is desirable. On the other hand, in order to increase the mechanical strength of the porous copper sintered film and the adhesion to the substrate, the porosity should be reduced. It is not preferable to raise more than necessary.

(Iii-1) Porosity A porous copper sintered film having a porosity of 40 to 70% can be obtained by the above production method.
In the first embodiment, the porosity of the sintered porous copper film is a value calculated from the density obtained by dividing the weight of the sintered body by its outer volume as the bulk density.
The porous copper sintered film having a porosity of 40 to 70% can be controlled by selecting the concentration of copper fine particles in the copper fine particle dispersion (L), the thickness of the coating film on the substrate, and the rapid heating conditions. It is.
(Iii-2) Light Transmittance A porous copper sintered film having a light transmittance in the film thickness direction of light having a wavelength of 460 nm of 30%, preferably 50% or more can be obtained by the above production method. The higher the transmittance, the more preferable.
In the first aspect, the light transmittance of the porous copper sintered film is as follows: (a) The light of 460 nm, which is the wavelength with the highest luminance of the white LED as the backlight of the liquid crystal display, is used. Measure the light intensity (Ls) in the film thickness direction of the porous copper thin film formed above and the light intensity (Lr) through only the glass substrate, and (b) form on the glass substrate. It is a value (Ls / Lr) obtained by dividing the intensity (Ls) of light passing in the thickness direction of the porous thin copper film by the intensity (Lr) of light passing only through the glass substrate. The intensity of such transmitted light can be measured using a spectrophotometer.

(Iii-3) Sheet Resistance Value According to the above production method, the sheet resistance value of the porous copper sintered film is preferably 0.01 to 5 (Ω / □), more preferably 0.01 to 1 (Ω / □). A certain porous copper sintered film can be obtained. More preferred is 0.01 to 0.1 (Ω / □). In the first aspect, the sheet resistance value of the porous copper sintered film is a value measured by a four-terminal sheet resistance measurement in accordance with JIS K7194 (resistivity test method using a four-probe method of conductive plastic). is there.

[2] About “Porous Copper Sintered Membrane” as Second Aspect “Porous Copper Sintered Membrane” as the second embodiment is a method in which copper fine particles having an average primary particle size of 1 to 500 nm are sintered. The porosity obtained is 40 to 70%, the light transmittance in the thickness direction of light having a wavelength of 460 nm is 30% or more, and the sheet resistance is 0.01 to 5 (Ω / □). And
Hereinafter, the porous copper sintered film of the present invention will be described.
(1) Copper fine particles having an average primary particle diameter of 1 to 500 nm The porous copper sintered film in the second aspect is formed by sintering copper fine particles having an average primary particle diameter of 1 to 500 nm. If so, the production method is not particularly limited. For example, as described later, the copper fine particle dispersion can be applied to a substrate and then sintered in an inert gas atmosphere. Thus, when forming a porous copper sintered film by sintering a copper fine particle dispersion solution, it is possible to manufacture by arbitrarily controlling the porosity and film thickness.
The copper fine particles are fine particles having an average primary particle diameter of 1 to 500 nm.
Here, the average particle size of the primary particles means the diameter of the primary particles of the copper fine particles constituting the secondary particles. The diameter of the primary particles can be measured using a transmission electron microscope (TEM). Moreover, an average particle diameter means the number average particle diameter of a primary particle. The average primary particle size of the fine particles is 1 to 500 nm, but from a practical aspect such as production and handling, fine particles of 1 to 100 nm are preferable.
In addition, as the transparent particles, one or more selected from silica particles alone and a metal oxide group of Zr, Ti, Sn, Ce, Ta, Nb, and Zn can be added to the copper fine particles. . Moreover, the preferable average particle diameter is 0.5-10 micrometers, and it is preferable that the addition amount shall be 0.1-30 wt% in all the particles containing a copper microparticle.

(2) Porosity The porosity of the “porous copper sintered film” is 40 to 70%.
The porosity of the porous copper sintered film in the second embodiment is a value calculated from the density obtained by dividing the weight of the sintered body by its outer volume as the bulk density.
The voids in the porous copper sintered film need to be continuously opened to the outside of the sintered film three-dimensionally in order to increase the light transmittance. On the other hand, a higher porosity is desired to increase the mechanical strength of the porous copper sintered film and the adhesion to the substrate.
The porous copper sintered film having a porosity of 40 to 70% can be controlled by selecting the concentration of copper fine particles in the copper fine particle dispersion (L), the thickness of the coating film on the substrate, and the rapid heating conditions. However, a porous copper sintered film having a porosity of 60 to 70% is preferred for use as a transparent conductive film in the field of flat panel displays such as LCD and organic EL.

(3) Light transmittance The light transmittance in the film thickness direction of light having a wavelength of 460 nm of the porous copper sintered film in the second aspect is 30% or more, preferably 50% or more. The higher the transmittance, the more preferable.
The light transmittance of the porous copper sintered film in the second aspect is (i) formed on a glass substrate using light of 460 nm, which is the wavelength with the highest luminance of the white LED that is the backlight of the liquid crystal display. The intensity (Ls) of light passing through the thickness direction of the porous thin copper film and the intensity (Lr) of light passing only through the glass substrate were respectively measured. It is a value (Ls / Lr) obtained by dividing the intensity (Ls) of light passing in the thickness direction of the porous copper thin film formed above by the intensity (Lr) of light passing only through the glass substrate. A known spectrophotometer can be used for measuring the intensity of transmitted light.

(4) Sheet resistance value The sheet resistance value of the porous copper sintered film in the second embodiment is 0.01 to 5 (Ω / □), preferably 0.01 to 1 (Ω / □). More preferred is 0.01 to 0.1 (Ω / □).
In addition, the sheet resistance value of the porous copper sintered film in the second aspect was measured by using a four-terminal sheet resistance measurement in accordance with JIS K7194 (resistivity test method using a four-probe method of conductive plastic). Value.

(5) Thickness of porous copper sintered film The thickness of the porous copper sintered film in the second aspect is preferably in the range of 50 nm to 10 μm. Moreover, from a light-transmissive viewpoint, More preferably, it is 50 nm-5 micrometers, More preferably, it is 50 nm-500 nm. In addition, the thickness of the porous copper sintered film in the second embodiment is a value measured using a scanning electron microscope (SEM), measured at any five points, and the average value is the average thickness. And

(6) Density The density of the porous copper sintered film in the second aspect is preferably in the range of 1.5 to 5.5 g / cm ³ . Furthermore, the range of 1.5-3.5 g / cm < ³ > is more preferable. The density of the sintered porous copper film is a value measured based on the apparent density measurement method (JIS C2141).
(7) Applications The porous copper sintered film of the present invention can be widely used as a transparent conductive film for flat panel displays (FPD) such as liquid crystal displays (LCD) and organic electroluminescence (organic EL).

Next, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.
The evaluation method and evaluation criteria are as follows.
(1) Average thickness of porous copper sintered film It measured using the scanning electron microscope (SEM; Scanning Electron Microscope). Measurement was performed on arbitrary five points, and the average value was defined as the average thickness.
(2) Porosity The porosity of the porous copper sintered film is a value calculated from the density obtained by dividing the weight of the sintered body by its outer volume as the bulk density.

(3) Light transmittance The white LED, which is the backlight of the liquid crystal display, passed through the porous copper sintered film formed on the glass substrate in the thickness direction using 460 nm light, which has the highest luminance. The light intensity (Ls) and the light intensity (Lr) passing through only the glass substrate were measured. The light transmittance is a value obtained by dividing the intensity (Ls) of light passing in the thickness direction of the porous copper sintered film formed on the glass substrate by the intensity (Lr) of light passing only through the glass substrate. Calculated as (Ls / Lr). The spectrophotometer used is a model: U-4100 type solid sample measuring system manufactured by Hitachi High-Technologies Corporation.
Evaluation criteria are as follows.
◎: Light transmittance is 50% or more ○: Light transmittance is 30% or more and less than 50% ×: Light transmittance is less than 30%

(4) Sheet resistance Measured using JIS K7194 (resistivity test method by 4-probe method for conductive plastics) using “4-terminal sheet resistance measurement (Mitsubishi Chemical Corporation, model: Loresta G P)” did.
Evaluation criteria are as follows.
◎ Less than 1 (Ω / □) ○: 1 (Ω / □) or more, 5 (Ω / □) or less ×: More than 5 (Ω / □)

[Example 1]
(1) Preparation of a copper particle dispersion solution In 180 ml (ml) of a reducing agent aqueous solution in which sodium borohydride as a reducing agent is dissolved at a concentration of 0.017 mol / liter, polyvinylpyrrolidone (number average) as a dispersing agent is added. 1.0 g of molecular weight 3500) was added and stirred, and then 0.6 g of copper acetate ((CH ₃ COO) ₂ Cu · H ₂ 0) was dissolved in 20 ml of distilled water in the reducing agent aqueous solution in a nitrogen gas atmosphere. The obtained aqueous solution was dropped, and then stirred at 40 ° C. for about 5 minutes, and at least a part of the surface of the copper fine particles having a primary particle size of 80 to 180 nm was covered with a dispersant. Got.
100 ml of an aqueous solution having a copper fine particle concentration of 1 mg / ml was bubbled with oxygen to aggregate the copper fine particles. Aggregated copper fine particles were collected by centrifugation. After 80 mg of the collected copper fine particles are dispersed in 2.5 ml of an ethylene glycol solution which is a redispersion solvent, stirring is performed by ultrasonic irradiation for 20 minutes at room temperature, and the copper fine particles are dispersed in the ethylene glycol solvent at a concentration of 3% by mass. A copper particle dispersion solution (L1) was obtained. In addition, the stirring method was performed using the general purpose magnetic stirrer.

(2) Production of porous copper sintered film 0.22 ml of copper fine particle dispersion solution (L1) was dropped onto a glass substrate (area: 26 mm × 19 mm) sufficiently cleaned using ultrasonic waves to disperse copper fine particles. A glass substrate coated with the solution (L1) was obtained. After fixing the glass substrate coated with the copper fine particle dispersion solution in a glass tubular container (outer diameter: 120 mm, length: 1200 mm), nitrogen gas was circulated in the glass tube to make the inside of the glass tube a nitrogen gas atmosphere. . Next, while flowing nitrogen gas, the glass tubular container was inserted into an electric tubular furnace heated to 250 ° C. (built-in nichrome wire heater, inner diameter 150 mm) and held for 15 minutes. Sintered. After the glass tubular container is removed from the electric tubular furnace and cooled to room temperature, the flow of nitrogen gas into the glass tubular container is stopped, and a glass substrate having a porous copper sintered film formed on the surface is formed from the glass tubular container. The material (sample A) was pulled out.

(3) Evaluation of porous copper sintered film About the obtained sample A, the film thickness, the porosity, the light transmittance in the thickness direction of light having a wavelength of 460 nm, and the sheet resistance were evaluated. The results are summarized in Table 1.
The voids in the porous copper sintered film need to be continuously opened to the outside of the sintered film three-dimensionally in order to increase the light transmittance. On the other hand, a higher porosity is desired to increase the mechanical strength of the porous copper sintered film and the adhesion to the substrate.

[Examples 2 and 3]
(1) Preparation of Copper Particle Dispersion Solution In Example 2 and 3, a copper particle dispersion solution in which copper fine particles are dispersed in an ethylene glycol solvent at a concentration of 3% by mass in the same manner as described in Example 1 ( L1) was used.
(2) Production of porous copper sintered film In Examples 2 and 3, the examples except that 0.20 ml and 0.14 ml of the copper fine particle dispersion (L1) were respectively dropped onto the glass substrate (area: 26 mm × 19 mm). Glass substrates coated with the copper fine particle dispersion (L1) were obtained in the same manner as described in 1. After fixing the glass substrate coated with each copper fine particle dispersion solution in a glass tubular container in the same manner as described in Example 1, nitrogen gas was circulated in the glass tube to bring the inside of the glass tube into a nitrogen gas atmosphere. did. Next, in Examples 2 and 3, the glass tubular container was inserted into an electric tubular furnace heated to 280 ° C. and 330 ° C. while nitrogen gas was circulated, and held for 15 minutes. Was sintered. After the glass tubular container is removed from the electric tubular furnace and cooled to room temperature, the flow of nitrogen gas into the glass tubular container is stopped, and a glass substrate having a porous copper sintered film formed on the surface is formed from the glass tubular container. The material (sample B) and (sample C) were extracted.
(3) Evaluation of porous copper sintered film The obtained samples B and C were evaluated in the same manner as the method described in Example 1. The results are summarized in Table 1. Moreover, the scanning electron microscope (SEM; Scanning Electron Microscope) photograph of the porous copper sintered film obtained in Example 3 is shown as a perspective view in FIG.

[Comparative Example 1]
(1) Preparation of Copper Particle Dispersion Solution A copper particle dispersion solution (L1) in which copper fine particles are dispersed in an ethylene glycol solvent at a concentration of 3% by mass by the same method as described in Example 1 was used.
(2) Preparation of porous copper sintered film The copper fine particle dispersion solution (L1) was prepared in the same manner as described in Example 1 except that 0.36 ml was dropped onto a glass substrate (area: 26 mm × 19 mm). A glass substrate coated with the fine particle dispersion (L1) was obtained. After fixing the glass substrate coated with the copper fine particle dispersion solution in a glass tubular container in the same manner as described in Example 1, nitrogen gas was circulated in the glass tube to make the inside of the glass tube a nitrogen gas atmosphere. After inserting into an electric tubular furnace at room temperature, the ethylene glycol solvent used was evaporated and removed by a drying operation in which the temperature was raised to 170 ° C. over 45 minutes and maintained at that temperature for 1 hour. Then, it heated up to 250 degreeC over 45 minutes, and hold | maintained at the temperature for 1 hour, and sintered copper fine particle. Next, the glass tubular container was pulled out from the electric tubular furnace to obtain a glass substrate (sample D) having a porous copper sintered film formed on the surface.
(3) Evaluation of porous copper sintered film About the obtained sample D, evaluation similar to the method described in Example 1 was performed. The results are summarized in Table 1. Moreover, the electron microscope (SEM) photograph of the porous copper sintered film obtained in Comparative Example 1 is shown in FIG. 2 as a perspective view.

From Table 1, as in Comparative Example 1, the dispersion of the metal fine particles applied on the substrate is first heated in the drying step to remove the solvent, and then the metal fine particles are sintered at a high temperature in the sintering step. In this case, the sheet resistance value is good and the conductivity is excellent, but it is understood that the porosity is low and there is almost no light transmittance. On the other hand, as in Examples 1 to 3, without providing a drying step, by inserting the copper fine particle dispersion applied on the substrate into a heated furnace, the porosity is maintained while maintaining conductivity. It is 40% or more, and it can be seen that it has light transmittance.
Further, as in Example 3, by increasing the sintering temperature, the porosity can be increased, and a porous copper sintered film having more excellent permeability can be formed.

[Examples 4 and 5]
(1) Preparation of copper particle dispersion solution The method described in Example 1 except that a mixed solvent consisting of 30% by volume of ethylene glycol and 70% by volume of N-methylformamide was used instead of the ethylene glycol solution as the redispersion solvent. In the same manner, a copper particle dispersion solution (L2) was obtained in which copper fine particles were dispersed in an ethylene glycol-N-methylformamide mixed solvent at a concentration of 3% by mass.
(2) Production of porous copper sintered film In Example 4, 0.004 ml of the copper fine particle dispersion (L2) was dropped onto a glass substrate (area: 26 mm × 19 mm) and spin-coated. 0.03 ml of the copper fine particle dispersion (L2) was dropped onto a glass substrate (area: 26 mm × 19 mm) and spin-coated to obtain a glass substrate coated with the copper fine particle dispersion (L2). After fixing the glass substrate coated with each copper fine particle dispersion solution in a glass tubular container similar to the method used in Example 1, nitrogen gas was circulated in the glass tube to bring the glass tube into a nitrogen gas atmosphere. did. Next, the glass tubular container was inserted into an electric tubular furnace heated to 280 ° C. while nitrogen gas was circulated, and held for 15 minutes to sinter the copper fine particles on the glass substrate. After the glass tubular container is removed from the electric tubular furnace and cooled to room temperature, the flow of nitrogen gas into the glass tubular container is stopped, and a glass substrate having a porous copper sintered film formed on the surface is formed from the glass tubular container. The material (sample E) and (sample F) were extracted.
(3) Evaluation of porous copper sintered film The obtained samples E and F were evaluated for film thickness, porosity, light transmittance in the thickness direction of light having a wavelength of 460 nm, and sheet resistance. The results are summarized in Table 2.

[Examples 6 and 7]
(1) Preparation of copper particle dispersion solution In Examples 6 and 7, copper fine particles were dispersed in an ethylene glycol-N-methylformamide mixed solvent at a concentration of 3% by mass in the same manner as described in Example 4. Each copper particle dispersion solution (L2) was used.
(2) Production of porous copper sintered film In Example 6, 0.26 ml of the copper fine particle dispersion (L2) was dropped onto a glass substrate (application area: 26 mm × 19 mm). A glass substrate coated with the copper fine particle dispersion (L2) in the same manner as described in Example 1 except that 0.39 ml of the solution (L2) was dropped onto a glass substrate (application area: 26 mm × 19 mm). Each material was obtained. After fixing the glass substrate coated with each copper fine particle dispersion solution in a glass tubular container in the same manner as described in Example 1, nitrogen gas was circulated in the glass tube to bring the inside of the glass tube into a nitrogen gas atmosphere. did. Next, in Examples 6 and 7, the glass tubular container was inserted into an electric tubular furnace heated to 300 ° C. and 350 ° C. while nitrogen gas was circulated, and held for 15 minutes. Was sintered. After the glass tubular container is removed from the electric tubular furnace and cooled to room temperature, the flow of nitrogen gas into the glass tubular container is stopped, and a glass substrate having a porous copper sintered film formed on the surface is formed from the glass tubular container. The material (sample G) and (sample H) were extracted.
(3) Evaluation of porous copper sintered film About the obtained samples G and H, the same evaluation as the method described in Example 1 was performed. The results are summarized in Table 2. Moreover, the electron microscope (SEM) photograph of the porous copper sintered film obtained in Example 6 is shown in FIG. 3 as a perspective view.

[Example 8]
(1) Preparation of Copper Particle Dispersion Solution In Example 8, copper in which copper fine particles are dispersed in an ethylene glycol-N-methylformamide mixed solvent at a concentration of 3% by mass in the same manner as described in Example 4 In the particle dispersion solution (L2), transparent silica particles having an average particle diameter of 3 μm as transparent particles mixed with one-fifth of the copper fine particle weight and stirred for 30 minutes with an ultrasonic cleaner were used.
(2) Production of porous copper sintered film In Example 8, the method described in Example 1 except that 0.3 ml of the copper fine particle dispersion (L2) was dropped onto a glass substrate (application area: 26 mm × 19 mm). In the same manner as above, glass substrates coated with the copper fine particle dispersion (L2) were obtained. After fixing the glass substrate coated with each copper fine particle dispersion solution in a glass tubular container in the same manner as described in Example 1, nitrogen gas was circulated in the glass tube to bring the inside of the glass tube into a nitrogen gas atmosphere. did. Next, in Example 8, the glass tubular container was inserted into an electric tubular furnace heated to 300 ° C. while flowing nitrogen gas, and held for 15 minutes to sinter the copper fine particles on the glass substrate. After the glass tubular container is removed from the electric tubular furnace and cooled to room temperature, the flow of nitrogen gas into the glass tubular container is stopped, and a glass substrate having a porous copper sintered film formed on the surface is formed from the glass tubular container. The material (Sample I) was pulled out.
(3) Evaluation of porous copper sintered film About the obtained sample I, the same evaluation as the method described in Example 1 was performed. The results are summarized in Table 2. Moreover, it shows in FIG. 4 as an image figure of the porous copper sintered film obtained in Example 8. FIG.

[Comparative Example 2]
(1) Preparation of Copper Particle Dispersion Solution Copper particle dispersion solution (L2) in which copper fine particles are dispersed in an ethylene glycol-N-methylformamide mixed solvent at a concentration of 3% by mass in the same manner as described in Example 4. )
(2) Production of porous copper sintered film The same method as described in Example 1 except that 2.0 ml of the copper fine particle dispersion (L2) was applied to a glass substrate so that the application area was 26 mm × 19 mm. Thus, a glass substrate coated with the copper fine particle dispersion (L2) was obtained. After fixing the glass substrate coated with the copper fine particle dispersion solution in a glass tubular container similar to the method used in Example 1, nitrogen gas was circulated in the glass tube to make the inside of the glass tube a nitrogen gas atmosphere. Next, the glass tubular container was inserted into an electric tubular furnace heated to 350 ° C. while nitrogen gas was circulated, and held for 15 minutes to sinter the copper fine particles on the glass substrate. After the glass tubular container is removed from the electric tubular furnace and cooled to room temperature, the flow of nitrogen gas into the glass tubular container is stopped, and a glass substrate having a porous copper sintered film formed on the surface is formed from the glass tubular container. The material (sample J) was pulled out.
(3) Evaluation of porous copper sintered film About the obtained sample J, evaluation about the film thickness, the porosity, the light transmittance to the thickness direction of the light of wavelength 460nm, and sheet resistance was performed. The results are summarized in Table 2.

  From Table 2, in Comparative Example 2, when the thickness of the coating film is thicker than 3 mm, even if the sintering temperature is increased to 450 ° C., the porosity is less than 40%, and light transmittance can be secured. could not. In addition, when the thickness of the coating film is increased as in Example 7, the porosity can be increased by increasing the sintering temperature, but for further improvement of light transmission. I was not connected. On the other hand, as in Examples 4 and 5, by reducing the thickness of the coating film and reducing the thickness of the sintered film, it was found that the light transmittance was good even when the porosity was about 50%. . Further, in Example 8, it was confirmed that a film having low surface resistance and good light transmittance could be produced by mixed sintering with transparent fine particles.

Claims (17)

  A copper fine particle dispersion solution (L) dispersed in a solvent (S) so that copper fine particles having an average primary particle diameter of 1 to 500 nm are in a concentration of 2 to 70% by mass is applied to a substrate, and then The base material coated with the copper fine particle dispersion solution (L) is inserted into a furnace in an inert gas atmosphere heated to 160 to 500 ° C. and rapidly heated to sinter the copper fine particles to obtain a porosity. A method for producing a porous sintered copper film, comprising forming a sintered film of 40 to 70% on a substrate.   The base material coated with the copper fine particle dispersion (L) is housed in a container under an inert gas atmosphere and inserted into the heated furnace. A method for producing a porous sintered copper film.   The method for producing a porous copper sintered film according to claim 2, wherein the inert gas is nitrogen gas or argon gas, and the container is a glass container.   The method for producing a porous copper sintered film according to any one of claims 1 to 3, wherein the thickness of the coating solution on the substrate is in the range of 1 µm to 3 mm.   The porous copper sintered film according to any one of claims 1 to 4, wherein the porous copper sintered film has a light transmittance of 30% or more in the film thickness direction of light having a wavelength of 460 nm. Method.   The sheet resistance value of a porous copper sintered film is 0.01-5 ohm / square, The manufacturing method of the porous copper sintered film of any one of Claim 1 thru | or 5 characterized by the above-mentioned.   In the copper fine particle dispersion (L), at least a part of the surface of the copper fine particle is covered with a dispersant (including a polymer compound) selected from a compound consisting of a carbon atom, a hydrogen atom, an oxygen atom, and a nitrogen atom. The porous copper sintered film according to any one of claims 1 to 5, which is dispersed in a dispersion solvent (including a mixed solvent) (S) having a boiling point of 60 ° C or higher and 400 ° C or lower. Manufacturing method.   The dispersion solvent (S) is an organic solvent (S1) comprising an alcohol (A) having 1 and / or 2 or more hydroxyl groups in the molecule, or an alcohol (A) having 1 and / or 2 or more hydroxyl groups in the molecule (A The porous copper sintered film according to any one of claims 1 to 7, which is a mixed solvent (S2) containing 20 to 40% by volume and an organic solvent having an amide group (B) of 60 to 80% by volume. Manufacturing method.   The alcohol (A) is ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-butene- 1,4-diol, 2,3-butanediol, pentanediol, hexanediol, octanediol, glycerol, 1,1,1-trishydroxymethylethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol 1,2,6-hexanetriol, 1,2,3-hexanetriol, 1,2,4-butanetriol, threitol, erythritol, pentaerythritol, pentitol, and hexitol, or The production of a porous copper sintered film according to claim 8, wherein there are two or more kinds. Law.   The organic solvent (B) having the amide group is N-methylacetamide, N-methylformamide, N-methylpropanamide, formamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N, The one or more selected from N-dimethylformamide, 1-methyl-2-pyrrolidone, hexamethylphosphoric triamide, 2-pyrrolidinone, ε-caprolactam, and acetamide. Manufacturing method of porous copper sintered film.   Obtained by sintering copper fine particles having an average primary particle diameter of 1 to 500 nm, a porosity of 40 to 70%, and a light transmittance in the film thickness direction of light having a wavelength of 460 nm of 30% or more, and A porous copper sintered film having a sheet resistance value of 0.01 to 5Ω / □.   After applying a copper fine particle dispersion solution (L) in which copper fine particles having an average primary particle diameter of 1 to 500 nm are dispersed on a substrate, an inert gas atmosphere in a furnace heated to 160 to 500 ° C. The porous copper sintered film according to claim 11, which is obtained by sintering.   The porous copper sintered film according to claim 11 or 12, wherein the transmittance in the film thickness direction of light having a wavelength of 460 nm is 50% or more and the sheet resistance value is 0.01 to 5Ω / □. The porous copper sintered film according to any one of claims 11 to 13, wherein the density of the sintered film is 1.5 to 5.5 g / cm ³ .   The porous copper sintered film according to claim 11, wherein the sintered film has a thickness of 50 nm to 10 μm.   The porous copper sintered film according to any one of claims 11 to 15, which is used for a transparent conductive film for a flat panel display (FPD).   The porous sintered copper film according to any one of claims 11 to 16, wherein the sintered film is formed of a mixture of copper fine particles and transparent particles.