JP7506404B2 - METAL FILM PRODUCTION METHOD, METAL FILM FORMING COMPOSITION, AND METAL FILM LAMINATE - Google Patents

Description

The present disclosure relates to a method for producing a metal film, a composition for forming a metal film, and a metal film laminate.

Metal films or metal oxide films having excellent electrical and thermal conductivity are used for various purposes. Metal films or metal oxide films can be made to have optical transparency by reducing their thickness.
For example, a copper film having high electrical conductivity and antibacterial properties is useful for forming a conductive layer on a substrate surface, an electromagnetic shield, an antibacterial member, etc. In addition, a metal film has good thermal conductivity, and can function as a heat dissipation member when used in lighting equipment, etc.
Metal films or metal oxide films, particularly thin metal films having a thickness on the order of microns or nanometers, are generally formed by gas phase methods. However, since gas phase methods such as sputtering require large-scale equipment for film formation, various methods for producing metal films by wet methods have been investigated.

Commonly used wet methods for producing metal films include electrolytic plating and electroless plating, and any of these methods can form metal films with thicknesses on the order of microns.
However, in electrolytic plating, since a metal film is formed using a substrate as an electrode, electrical conductivity of the substrate is essential, and it is difficult to apply the method to substrates made of inorganic materials such as glass substrates.
According to the electroless plating method, a metal film can be deposited on a substrate made of an inorganic material. However, depending on the type of catalyst contained in the electroless plating solution, the physical properties of the formed metal film may be affected. For example, when the electroless plating solution contains a metal catalyst, the metal catalyst remains in the formed metal film, which may cause problems such as corrosion of the metal film.

The method of forming a metal film by applying a metal film-forming composition onto a substrate offers greater freedom in the selection of the composition of the metal film, the substrate, etc., compared to a method of precipitating a metal film onto a substrate by a wet method such as plating.
As a method for producing a copper nanoparticle dispersion that can be used in a copper paste agent or an electrodeposition solution for forming copper wiring in solar cells or the like, a method for producing copper nanoparticles has been proposed in which a first aqueous solution containing copper ions and citric acid is mixed with a second aqueous solution containing ascorbic acid to obtain a dispersion of copper nanoparticles (see Patent Document 1).
The present inventors have also previously proposed a composition for forming a metal film, which contains a metal complex having a specific structure and is useful for forming a metal film (see Patent Document 2).

JP 2017-71816 A International Publication No. 2017/134769

In the technology described in Patent Document 1, the obtained copper nanoparticles have the property of being difficult to oxidize, so that the decrease in electrical conductivity caused by oxides in the wiring is suppressed. However, when forming a metal film such as wiring using the obtained copper nanoparticles, it is necessary to sinter the layer formed from the copper nanoparticle dispersion in a nitrogen atmosphere at a temperature of 190°C or higher in order to remove the ascorbic acid attached to the copper nanoparticles. For this reason, the method described in Patent Document 1 makes it difficult to form a metal film such as wiring on a substrate other than a metal substrate that has poor heat resistance.

The metal film-forming composition described in Patent Document 2 is useful for forming a dense metal film. However, when manufacturing the metal film-forming composition, it was necessary to prepare it by dissolving a metal salt compound capable of forming a metal complex in a solvent. In addition, although the heating temperature in forming the metal film is kept lower than the conventional sintering temperature, heating to about 100°C is considered to be desirable for forming an electrically conductive metal film. Therefore, from the viewpoint of the manufacturing method, a method for obtaining the desired metal complex without going through a metal salt compound is desired. Furthermore, in consideration of the versatility of the substrate, a method for forming an electrically conductive metal film without heating is desired.

In recent years, various metal film-forming compositions for use in the fabrication of circuits using semiconductors have been studied. However, the current situation is that no practically satisfactory method for producing a metal film-forming composition or a metal film using a metal other than a semiconductor, such as copper, that has electrical conductivity and thermal conductivity has yet been obtained. Furthermore, all metal film-forming compositions require sintering or heat treatment at a temperature of 100°C or higher to form a dense metal film with electrical conductivity, and a method for forming a dense metal film without the need for heat treatment is desired.

An object of one embodiment of the present invention is to provide a method for producing a metal film that does not require a heat treatment at 100° C. or higher and that can easily form a dense metal film on any substrate.
An object of another embodiment of the present invention is to provide a metal film-forming composition that can easily form a dense metal film on any substrate without requiring a heat treatment at 100° C. or higher, and a metal film laminate having a metal film that is a cured product of the metal film-forming composition.

Means for solving the above problems include the following embodiments.
<1> A method for producing a metal film, comprising: a step of reacting at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine in a mixed liquid containing at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent; a step of preparing a composition for forming a metal film, the composition comprising the obtained metal precursor liquid and an organic reducing agent; and a step of applying the obtained composition for forming a metal film to a substrate.
<2> The method for producing a metal film according to <1>, which obtains a metal film having a content of a metal different from the metal contained in at least one selected from the group consisting of metal complexes and metal salts that is below the detection limit in analysis by X-ray diffraction.

<3> The method for producing a metal film according to <1> or <2>, wherein the step of obtaining the metal precursor liquid includes the steps of: storing an electrolytic solution containing at least one selected from ammonia and an amine in each of the pair of electrolytic solution tanks in a reaction apparatus including a pair of electrolytic solution tanks connected via a flow path including a filter that does not allow metal ions to pass therethrough but allows hydrogen ions to pass therethrough; arranging metal electrodes in positions where they are at least partially in contact with the electrolytic solution; connecting the pair of electrodes via a DC power source; and applying a voltage between the pair of electrodes by the DC power source to react the electrolytic solution with metal ions in the electrolytic solution tank in which the electrode to be an anode is immersed.
<4> The method for producing a metal film according to <3>, wherein the metal ions are copper ions, and the electrode is a copper electrode.
<5> The method for producing a metal film according to <3> or <4>, wherein the electrolytic solution contains ethylenediaminetetraacetic acid.

<6> The method for producing a metal film according to any one of <1> to <5>, wherein the organic reducing agent includes at least one selected from compounds having a carboxy group.
<7> The method for producing a metal film according to any one of <1> to <6>, wherein the organic reducing agent includes at least one selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid.
<8> The method for producing a metal film according to any one of <1> to <7>, wherein the step of applying the metal film-forming composition to a substrate includes at least one of a step of applying the metal film-forming composition to a substrate, a step of immersing a substrate in the metal film-forming composition, and a method of storing the metal film-forming composition inside a container-shaped base.
<9> The method for producing a metal film according to any one of <1> to <8>, further comprising a step of drying the metal film-forming composition applied to the substrate.
<10> The method for producing a metal film according to <9>, wherein the step of applying the metal film-forming composition to the substrate and the step of drying the metal film-forming composition applied to the substrate are performed multiple times.

<11> A composition for forming a metal film, comprising a metal precursor liquid containing a reaction product of at least one selected from the group consisting of metal complexes and metal salts with at least one selected from ammonia and amines, and at least one organic reducing agent selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid, wherein the content of metal ions contained in the metal precursor liquid per 100 parts by mass of the organic reducing agent is in the range of 50 parts by mass to 400 parts by mass.

<12> A metal film laminate having, on the non-conductive substrate, a metal film which is a cured product of a metal film-forming composition which comprises: a metal precursor liquid containing a reaction product of at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine, and at least one organic reducing agent selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid, wherein the content of metal ions contained in the metal precursor liquid per 100 parts by mass of the organic reducing agent is in the range of 50 parts by mass to 400 parts by mass.
<13> The metal film laminate according to <12>, wherein the metal film is a metal film in which a content of a metal different from a metal contained in at least one selected from the group consisting of a metal complex and a metal salt is equal to or lower than a detection limit in an analysis by X-ray diffraction.
<14> The metal film laminate according to <12> or <13>, wherein the non-conductive base material contains a resin having at least one of a deflection temperature under load defined in JIS K7191 (2015) and a continuous heat resistance temperature determined by a long-term heat resistance continuous test (UL-746B (2013)) of less than 150°C.

According to one embodiment of the present invention, it is possible to provide a method for manufacturing a metal film that does not require a heat treatment at 100° C. or higher and that can easily form a dense metal film on any substrate.
According to another embodiment of the present invention, it is possible to provide a metal film-forming composition that can easily form a dense metal film on any substrate without requiring a heat treatment at 100° C. or higher, and a metal film laminate having a metal film that is a cured product of the metal film-forming composition.

FIG. 2 is a schematic diagram showing an example of a reaction apparatus used for preparing a metal precursor liquid in the metal film production method of the present disclosure. 1 shows XRD patterns of copper films formed on a quartz glass plate by the manufacturing methods of Examples 1 and 2. 1A is a cross-sectional FE-SEM image of a copper film formed on a quartz glass plate by the manufacturing method of Example 1, and FIG. 1B is a cross-sectional FE-SEM image of a copper film formed on a quartz glass plate by the manufacturing method of Example 2. 1A is a surface FE-SEM image of a copper film formed on a quartz glass plate by the manufacturing method of Example 1, and FIG. 1B is a surface FE-SEM image of a copper film formed on a quartz glass plate by the manufacturing method of Example 2. 1 is a schematic cross-sectional view showing an example of a copper film formed in a one-end sealed glass tube by the method of the present disclosure, and a measurement terminal attached to the copper film for measuring the internal resistance of the copper film.

The method for manufacturing a metal film according to the present disclosure will be described in detail below with reference to specific embodiments. The present disclosure is not limited to the following embodiments, and can be implemented in various modified forms as long as they do not deviate from the spirit of the disclosure.

In the present disclosure, a numerical range described using "to" indicates a numerical range that includes the numerical values before and after "to" as the lower and upper limits.
In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.
In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified.
In the present disclosure, the upper or lower limit of a certain numerical range described in a stepwise manner may be replaced with the upper or lower limit of another stepwise described numerical range. In addition, in the present disclosure, the upper or lower limit of a certain numerical range may be replaced with a value shown in the examples.
Also, in the present disclosure, combinations of two or more preferred aspects are more preferred aspects.
In this disclosure, unless otherwise specified, room temperature and normal temperature mean 25°C.

<Metal Film Manufacturing Method>
The method for producing a metal film according to the present disclosure (hereinafter, sometimes simply referred to as "the method for producing the metal film according to the present disclosure") includes a step of reacting at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine in a mixed liquid containing at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent to obtain a metal precursor liquid (step I), a step of preparing a composition for forming a metal film containing the obtained metal precursor liquid and an organic reducing agent (step II), and a step of applying the obtained composition for forming a metal film to a substrate (step III).

(Step I)
In step I, in a mixed liquid containing at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent, the at least one selected from the group consisting of a metal complex and a metal salt is reacted with the at least one selected from ammonia and an amine to obtain a metal precursor liquid.

-At least one selected from the group consisting of metal complexes and metal salts-
The mixed liquid contains at least one selected from the group consisting of metal complexes and metal salts.
At least one selected from the group consisting of metal complexes and metal salts may hereinafter be collectively referred to as a specific metal compound.
When the mixed liquid contains a metal complex, the metal complex reacts with at least one selected from ammonia and amines present in the mixed liquid.
When the mixed liquid contains a metal salt, the metal salt may dissociate in the mixed liquid containing the solvent to become metal ions, and the metal ions may react with at least one selected from ammonia and amines present in the mixed liquid to form a metal complex.
The mixture may contain both a metal complex and a metal salt.

A "metal salt" is a metal compound that has the function of being able to dissociate in a solvent containing water to become metal ions and form a metal complex.
In the present disclosure, the term "metal salt" refers to a metal salt that is soluble in water at 25° C. Soluble in water at 25° C. means that the solubility in water at 25° C. is 0.1% by mass or more, and the solubility is preferably 1% by mass or more.
Since the metal salt is soluble in water, the metal salt dissociates in a solvent containing water to become a metal ion, and the metal ion reacts with an amine contained in the solvent to obtain a metal complex. Furthermore, when a compound for forming a complex described below is optionally contained in the solvent, the metal ion may react with the compound for forming a complex to form a metal complex.

The metal complex that may be contained in the mixed liquid is preferably a reaction product between a metal ion and one or more compounds for forming a metal complex selected from compounds having, as a partial structure, an _NH3 ligand, an _RNH2 ligand (R represents an alkylene group), an _OH2 ligand, and a ligand derived from a diamine such as ethylenediamine or hexamethylenediamine, which are capable of generating a metal complex.
As the metal complex, a metal complex previously produced by the above reaction can be used.
The metal in the metal complex may be selected from metals that correspond to the purpose of the metal film to be formed, such as silver (Ag), copper (Cu), lithium (Li), nickel (Ni), manganese (Mn), zinc (Zn), and cobalt (Co).
When the mixed solution contains a metal complex, examples of the metal complex preferably include copper (Cu)-containing ethylenediaminetetraacetate, tetraammine copper, etc. From the viewpoint of good electrical and thermal conductivity of the formed metal film, Cu, Ag, etc. are preferred, and Cu is more preferred.
Specific preferred examples of metal complexes include copper (Cu)-containing ethylenediaminetetraacetate and tetraamminecopper.

When the mixed liquid contains a metal salt, the metal salt can react with at least one selected from ammonia and amines contained in the mixed liquid to form a metal complex, as described above.
For example, when the mixed liquid contains copper formate as a metal salt and ammonia which is included in the amines described below, the copper ions derived from the copper formate react with excess ammonia in the mixed liquid to produce tetraammine copper, which is a metal complex.

Furthermore, by further including in the mixed solution one or more compounds for forming a metal complex selected from compounds capable of reacting with metal ions to form a metal complex, for example, compounds having, as a partial structure, an _NH3 ligand, an _RNH2 ligand (R represents an alkylene group), an _OH2 ligand, or a ligand derived from a diamine such as ethylenediamine or hexamethylenediamine, a metal complex having a desired ligand can be formed in the mixed solution.
More specifically, the compound for forming a metal complex may be at least one selected from ammonia, ammonium formate, and ethylenediaminetetraacetic acid (structure shown below, hereinafter sometimes referred to as H ₄ EDTA), and these compounds are preferably contained in the mixed solution as an aqueous solution. In particular, it is more preferable that the mixed solution contains an aqueous solution of H ₄ EDTA as the compound for forming a metal complex.

The metal in the metal salt may be selected according to the metal film to be formed, similarly to the metal in the metal complex. Metals according to the purpose of the metal film to be formed include Ag, Cu, Li, Ni, Mn, Zn, Co, etc., and from the viewpoint of good electrical and thermal conductivity of the metal film to be formed, Cu, Ag, etc. are preferred, and Cu is more preferred.
When forming a metal complex derived from a metal salt in the mixed solution, it is preferable that the mixed solution contains a metal salt that is likely to become a metal ion. Examples of the metal salt that contains copper and is likely to become a copper ion in the solvent include copper formate, copper acetate, and copper chloride.
The mixed liquid may contain only one type of specific metal compound, or may contain two or more types.

Even when the mixed liquid contains only one type of metal salt, by further containing a compound for forming a metal complex, for example, ethylenediamine, the mixed liquid will contain two types of specific metal compounds having different ligands, namely, a metal complex which is a reaction product of a metal salt with amines, and a metal complex which is a reaction product of a metal salt with ethylenediamine.
When the mixed liquid contains two or more specific metal compounds, it may contain both a metal salt and a pre-prepared metal complex, or it may contain two or more pre-prepared metal complexes having different ligands.
In addition, when the mixed solution contains two or more specific metal compounds, for example, a combination of metal complexes containing the same metal but different ligands may be used, or a combination of metal complexes containing different metals may be used. In terms of synthesis suitability, a combination of metal complexes containing the same type of metal is preferable.

-At least one selected from ammonia and amines-
The mixed liquid contains at least one selected from ammonia and an amine.
The amine in the present disclosure includes primary amines, secondary amines, and tertiary amines. Examples of the amine include alkylamines. The mixed liquid may contain ammonia instead of or in addition to the amine. Since ammonia has the same basicity as the amine, hereinafter, at least one selected from ammonia and amines may be collectively referred to as "amines."
The amines may be contained in the mixed liquid as salt compounds.
The mixed liquid may contain only one type of amine, or may contain two or more types of amines.
The amines have basicity and react with the specific metal compound in the mixed liquid to obtain a metal precursor liquid.

-solvent-
The mixture includes a solvent.
As a solvent for dissolving the specific metal compound and amines, an aqueous solvent such as water or a mixture of water and alcohol can be used.
The water preferably contains a small amount of impurities, particularly ions other than metal ions, and from this viewpoint, it is preferable to use purified water, ion-exchanged water, pure water, or the like.
Examples of the alcohol include monohydric alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, isopropanol, n-propanol, isobutanol, and n-butanol, and polyhydric alcohols, such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, and glycerin.

From the viewpoint of the solubility and handling properties of the specific metal compound, the aqueous solvent is preferably water or a mixture of water and a monohydric alcohol having 1 to 5 carbon atoms, more preferably water or a mixture of water and an alcohol selected from methanol, ethanol and propanol, and even more preferably water.
When a mixture of water and alcohol is used as a solvent, the mixing ratio is appropriately selected depending on the purpose. When a mixture of water and alcohol is used as a solvent, the content of alcohol relative to the total amount of the mixture of water and alcohol is preferably 1% by mass to 60% by mass.
According to the manufacturing method of the present disclosure, even when water is used as the solvent, a uniform metal precursor liquid containing a specific metal compound can be obtained, and by using the obtained metal precursor liquid, a dense metal film can be formed through the steps described below, which is also one of the advantages of the manufacturing method of the present disclosure.

- Preparation of metal precursor liquid -
The metal precursor liquid can be prepared by adding a specific metal compound and amines to a solvent and thoroughly stirring and mixing the mixture.
The mixing may be carried out at room temperature, or the solvent may be heated to 40° C. to 60° C. in order to promote dissolution.
As the stirring method, a known stirring method can be applied. Examples of the stirring method include a method of putting a solution containing a specific metal compound and amines into a container and stirring with a rotor such as a magnetic stirrer, a method of stirring with a stirring device equipped with a rotary stirring blade such as a paddle, a method of putting the solution into a sealable container and stirring by shaking the container, and a method of irradiating with ultrasonic waves.
A simple method is to use a stirring device equipped with stirring blades. The rotation speed of the rotor blades can be 300 rpm (revolutions/minute: the same applies below) to 800 rpm, and preferably 400 rpm to 600 rpm.
It is preferable to carry out stirring until the reaction between the specific metal compound and the amines has sufficiently progressed. When stirring is carried out at room temperature using the above-mentioned stirring device equipped with a rotor blade, stirring is preferably carried out for about 30 to 90 minutes, and more preferably for about 50 to 80 minutes.
For example, when preparing a metal precursor liquid containing a copper complex, the metal precursor liquid that has been thoroughly stirred exhibits a blue color due to the copper ions.

Step I may be a step of obtaining a metal precursor by reacting a specific metal compound with amines using a known molecular precursor method.

In step I of the production method according to the present disclosure, a known precursor method can be applied as described above. However, from the viewpoint of obtaining a metal precursor with higher purity, it is preferable that step I includes the following step (hereinafter, sometimes referred to as "step I-2").
Step I-2 is a step of storing an amine-containing electrolytic solution in each of the pair of electrolytic solution tanks in a reaction apparatus equipped with a pair of electrolytic solution tanks connected via a flow path equipped with a filter (hereinafter, sometimes simply referred to as a "filter") that does not allow metal ions to pass therethrough but allows hydrogen ions to pass therethrough, and of connecting the pair of electrodes via a DC power source by arranging a metal electrode in a position where at least a portion of the electrode is in contact with the electrolytic solution, and of applying a voltage from the DC power source between the pair of electrodes to react metal ions derived from the metal electrode with the electrolytic solution in the electrolytic solution tank in which the electrode to be the anode is immersed, thereby obtaining a metal precursor liquid.

Step I-2 will now be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of a reaction apparatus used in the preparation of a metal precursor liquid, which is step I-2, in the method for producing a metal film according to the present disclosure.
The reaction device 10 shown in FIG. 1 includes a pair of electrolyte tanks 16, 18 for storing an electrolyte, which are connected via a flow path 14 having a filter 12 that is impermeable to metal ions but permeable to hydrogen ions.
The electrolyte tank 16 and the electrolyte tank 18 are each used to store an electrolyte 20 .

(A filter that blocks metal ions but allows hydrogen ions to pass through)
Due to the function of the filter 12 provided in the flow path 14 connecting the pair of electrolytic solution tanks 16, 18, the process I including the process I-2 can more efficiently produce the metal precursor, and thus the composition for forming a metal film.
There are no particular limitations on the filter 12 as long as it is a semipermeable membrane filter that does not allow metal ions to pass through but allows hydrogen ions to pass through. That is, the filter in the present disclosure is a filter that has a function of controlling whether or not ions pass through depending on the size of the ions.
Examples of filters include semipermeable membranes selected from cellulosic filters such as regenerated cellulose membrane (cellophane), acetyl cellulose membrane, and collodion membrane; ceramic filters such as unglazed plates and porous ceramics; porous membranes such as polyacrylonitrile, polysulfone, and polyester-based polymer alloys; and membrane filters containing fluororesin and cellulose acetate.
Examples of commercially available products include Visking Tube, available from Nippon Medical Science Co., Ltd., which is a commercially available cellulose filter used in artificial dialysis.
From these semipermeable membranes, an appropriate one can be selected and used as the filter in step I-2, taking into consideration the metal that forms the target metal membrane, specifically, the size of the metal ions that form the target metal membrane.
Among these, from the viewpoint of good durability even when constantly in contact with the electrolyte, a cellulose filter selected from a ceramic filter, a cellulose tube for dialysis, etc. is preferable.
There are no particular limitations on the type and thickness of the filter, so long as the filter can suppress the permeation of metal ions, more specifically, metal ions generated by applying a direct current to a metal that functions as an electrode, as described below.

Next, an electrolyte solution 20 containing amines is stored in each of the pair of electrolyte tanks 16, 18, and metal electrodes 22, 24 are placed in positions where at least a portion of the electrodes is in contact with the electrolyte solution 20, and the pair of electrodes 22, 24 are connected via a DC power source 26.
The storing of the electrolyte in each of the pair of electrolyte tanks 16, 18 and the disposition of the electrodes 22, 24 in each of the pair of electrolyte tanks 16, 18 may be performed in either order, or may be performed simultaneously. For the purpose of generating metal ions by applying a voltage as described below, the electrodes 22, 24 are disposed at positions where at least a portion of them contacts the electrolyte 20 stored in the electrolyte tanks 16, 18.

(electrode)
The metal used for the electrode may be selected according to the metal film to be formed by the manufacturing method of the present disclosure. As described above, the metal used for the electrode may include silver (Ag), copper (Cu), lithium (Li), nickel (Ni), manganese (Mn), zinc (Zn), cobalt (Co), etc. From the viewpoint of easy generation of metal ions and good electrical and thermal conductivity of the formed metal film, Cu, Ag, etc. are preferred for the electrode, and Cu is more preferred.
By using Cu as the electrode, copper ions are generated as metal ions in the electrolyte, which is preferable from the viewpoint of being useful for generating a copper film.
From the viewpoint of reactivity, it is preferable that the electrodes 22, 24 used in the pair of electrolyte cells 16, 18 are made of the same metal.

(Electrolyte)
The electrolyte used is one that can react with the generated metal ions to form a metal ion complex that is a metal precursor.
The electrolyte contains amines capable of forming a metal complex. The amines are the same as those described in the precursor method described in step I, and are preferably _one or more of compounds for forming a metal complex (hereinafter, sometimes referred to as a compound for forming a complex) selected from compounds having a ligand derived from a diamine such as NH ₃ ligand, RNH 2 ligand (R represents an alkylene group), ethylenediamine, hexamethylenediamine, etc. as a partial structure, and the amines are preferably contained in the electrolyte as an aqueous solution. In addition, the compound for forming a complex may include, in addition to the amines, the OH ₂ ligand listed as the compound for forming a metal complex described above.
More specifically, the complex-forming compound is preferably an aqueous solution containing at least one amine selected from ammonia, ammonium formate, and ethylenediaminetetraacetic acid (the above structure, H ₄ EDTA) included in amines, and more preferably an aqueous solution of H ₄ EDTA. The amines may be contained in the electrolyte as salt compounds.

The electrolytic solution used in step I-2 may contain only one type of complex-forming compound, such as amines, or may contain two or more types.
Among these, it is preferable to contain at least one type of ammonium derivative, such as ammonia having an _NH3 ligand or ammonium formate having an _RNH2 ligand, and at least one type of _H4EDTA having a ligand derived from a diamine.

As the solvent for the electrolyte in step I-2, the solvents described in step I that can be used as solvents for specific metal compounds, amines, etc., such as aqueous solvents such as water and mixtures of water and alcohol, can be used in the same manner.
Specific examples of the solvent usable in the present invention, such as water and alcohol, and preferred embodiments of the solvent for the electrolyte solution are the same as those described in the precursor method in step I.

The content of amines for complex formation in the electrolyte solution is preferably in the range of 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 10% by mass, and even more preferably 1.0% by mass to 8% by mass.

The electrolyte solution can be prepared by mixing and stirring water, which is a solvent, and a compound containing amines for forming a complex. The electrolyte solution may be prepared at room temperature (25° C.), or the solvent may be heated to 30° C. to 60° C. to promote dissolution.
It is preferable to continue stirring until the compound for complex formation is dissolved and the electrolyte solution becomes a visually homogeneous solution. When preparing the electrolyte solution at room temperature, it is preferable to stir for about 30 to 90 minutes, and more preferably for about 50 to 80 minutes.
The stirring can be carried out using a known stirring device, such as a stirrer, a paddle mixer, an impeller mixer, etc., but the stirring device is not limited to the above devices.

Next, a voltage is applied between the pair of electrodes 22, 24 by the DC power supply 26, and a metal precursor liquid containing a reaction product resulting from a reaction between the electrolytic solution and metal ions derived from the anode electrode is obtained in the electrolytic solution tank 16 in which the anode electrode 22 is immersed.
The previously prepared electrolytic solution is stored in a pair of electrolytic solution tanks 16, 18, and electrodes 22, 24 (e.g., copper plates) are arranged in positions where they are immersed in the electrolytic solution stored in the electrolytic solution tanks. A voltage is then applied between the electrode (anode) 22 and the electrode (cathode) 24 by a DC power source 26. The voltage applied can be greater than 0 V and equal to or less than 100 V, and is preferably in the range of 1 V to 80 V, and more preferably in the range of 10 V to 60 V.
The power supply may be selected from known DC power supplies as appropriate. Examples of known DC power supplies that may be used in the present disclosure include a DC stabilized power supply (PMC18-2, product name, Kikusui Electronics Co., Ltd.).

The general reaction when a direct current is applied to an electrode is similar to that in, for example, copper electrorefining.
For example, when the metal copper is used as the anode and the cathode, the metal of the anode is oxidized and dissolved as metal ions, and a reduction reaction occurs at the cathode. The reaction in this case is shown below.
Anode: Cu → Cu ²⁺ + 2e ⁻
Cathode: H ^{++ 2e-} → _H2

The above reaction also occurs when the same set of electrodes is placed in an electrolyte tank and a voltage is applied. If the reaction then progresses and the copper ion concentration in the electrolyte increases, the reaction Cu ²⁺ +2e ^- →Cu occurs preferentially at the cathode over the hydrogen (H ₂ ) production reaction over time. This is because the copper ions (Cu ²⁺ ) produced have a smaller ionization tendency than the hydrogen ions (H ⁺ ) produced at the cathode.
Therefore, as shown below, when the copper ion concentration in the electrolyte exceeds a predetermined amount, copper precipitates on the cathode side, the copper ion concentration in the electrolyte does not increase beyond the predetermined amount, and the efficiency of metal complex production tends to decrease over time when the voltage application is continued.
Anode: Cu → Cu ²⁺ + 2e ⁻
Cathode: Cu ²⁺ +2e ^- →Cu

In step I-2, which is a preferred embodiment of step I, a filter is provided in a flow path connecting a pair of electrolyte tanks. Therefore, metal ions generated in the electrolyte tank containing the anode do not move to the electrolyte tank containing the cathode, but remain in the electrolyte in the electrolyte tank containing the anode, and react with a complex-forming compound in the electrolyte to form a metal complex.
For example, when copper (Cu) is used as the metal and H ₄ EDTA is used as the compound for forming a complex, the following reaction occurs.
^Cu2 + + _H4EDTA → [Cu( _H2EDTA )] ^2- + 2H ⁺
On the other hand, the hydrogen ions produced in this reaction can permeate the filter and therefore move to the electrolyte tank on the side where the cathode is present, where the above-mentioned reaction "H ⁺ +2e ^- →H ₂ " proceeds, generating hydrogen.
Since the copper ions on the side where the anode is present are used to form a copper complex, it is believed that the reaction "Cu → Cu ²⁺ + 2e ^- " proceeds on the anode side, and a metal complex as a metal precursor is efficiently produced.
Therefore, in the production method of the present disclosure, by including step I-2, a metal precursor liquid that stably contains a metal precursor at a high concentration can be efficiently produced without going through an intermediate such as a metal salt compound.

(Step II)
Step II is a step of preparing a composition for forming a metal film, which contains the metal precursor liquid obtained in step I, which may include step I-2, and an organic reducing agent (hereinafter, sometimes referred to as a specific reducing agent).
In step II, it is preferable to prepare a composition for forming a metal film by mixing the metal precursor liquid obtained in step I with an aqueous solution containing a specific reducing agent described below.

- Metal precursor liquid -
The metal precursor liquid used in step II is the metal precursor liquid obtained in step I, specifically, a solution containing at least a specific metal compound and amines. The metal complex contained in the metal precursor liquid may be a reaction product of a metal salt and amines and, if desired, the above-mentioned compound for forming a metal complex, which is further contained, or may be a metal complex prepared in advance.
The metal precursor liquid may contain only one type of specific metal compound, or may contain two or more types of specific metal compounds.
When the metal precursor liquid contains two or more specific metal compounds that are metal precursors, it may be, for example, a combination of metal complexes containing the same metal but different ligands, a combination of metal complexes containing different metals, etc. In terms of synthesis suitability, it is preferable to use a combination of metal complexes containing the same type of metal.

-Specific reducing agent-
The specific reducing agent used in the preparation of the metal film-forming composition preferably contains at least one selected from compounds having a carboxy group. As the specific reducing agent, it is preferable to appropriately select and use an organic carboxylic acid compound having a carboxy group in the molecule and functioning as a reducing agent.

Examples of the specific reducing agent include at least one selected from ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid. From the viewpoint of better metal film formability, at least one selected from ascorbic acid, citric acid, and 3,4,5-trihydroxybenzoic acid is preferred, and at least one selected from ascorbic acid and citric acid is more preferred.
One of the preferred embodiments of the composition for forming a metal film of the present disclosure includes ascorbic acid as an organic reducing agent.

The specific reducing agent is preferably used as an aqueous solution.
From the viewpoint of uniformity of the obtained metal film, it is preferable that the water used for preparing the aqueous solution does not contain metal ions or has a metal ion concentration as low as possible. Therefore, it is preferable to use purified water, ion-exchanged water, pure water, etc. as the water used for preparing the aqueous solution.
When dissolving the specific reducing agent in water, for the purpose of improving solubility, the water as a solvent may be heated to 30° C. to 60° C., and is preferably heated to 35° C. to 45° C. The dissolution may be performed with stirring, and the stirring method mentioned in the above section on the method for preparing a solution of a metal complex can be appropriately applied in the same manner.
The content of the specific reducing agent in the aqueous solution of the specific reducing agent is preferably in the range of 10% by mass to 40% by mass, and more preferably in the range of 10% by mass to 30% by mass.
When the content of the specific reducing agent relative to the total amount of the aqueous solution is 10% by mass or more, the aqueous solution contains a sufficient amount of organic reducing agent for the reaction, and when the content is 40% by mass or less, the stability of the aqueous solution becomes better.

In step II, the contents of the metal precursor liquid and the organic reducing agent in the composition for forming a metal film obtained by mixing the metal precursor liquid and the solution of a specific reducing agent are not particularly limited and can be appropriately selected depending on the desired metal film.
The amount of metal ions contained in the metal precursor liquid can be 50 parts by mass to 400 parts by mass per 100 parts by mass of the specific reducing agent contained in the metal film-forming composition. In particular, from the viewpoint of improving the metal film formability of the resulting metal film-forming composition, it is preferable that the amount of metal ions contained in the metal precursor liquid is 100 parts by mass to 350 parts by mass per 100 parts by mass of the specific reducing agent, and it is more preferable that the amount of metal ions contained in the metal precursor liquid is 150 parts by mass to 350 parts by mass per 100 parts by mass of the specific reducing agent.

By setting the range of the content of metal ions relative to the specific reducing agent to the above-mentioned preferred range, a denser metal film can be formed more efficiently on the substrate. Although the mechanism of this action is not clear, the present inventors believe it to be as follows.
It is considered that the content of metal ions in the metal complex is more improved by 50 parts by mass or more relative to 100 parts by mass of the specific reducing agent, and the metal ions attached to the substrate are reduced to precipitate quickly, forming a dense metal film. In addition, it is considered that the content of metal ions in the metal complex is 400 parts by mass or less relative to 100 parts by mass of the specific reducing agent, and the deposition rate of metal caused by the reduction of metal ions is maintained in a good range, and the deposition of metal particles not attached to the substrate due to the redissolution of the deposited metal film is suppressed by ammonia or amine in the metal precursor compound.
Note that the above-mentioned mechanism of action is merely a presumption and does not in any way limit the manufacturing method of the present disclosure.

The obtained metal film-forming composition is useful for forming a metal film.
The content of the metal precursor liquid in the preparation of the metal film-forming composition can be controlled by adjusting the type and content of the metal complex when preparing the metal precursor liquid in step I, or the type of the electrolyte solution, the concentration of the electrolyte solution, the applied energy of the direct current, the application time, etc. in step I-2.
In general, it is difficult to measure the content of a specific metal compound relative to the total amount of a composition for forming a metal film. However, the physical properties of a metal film formed by the composition for forming a metal film depend on the content of the metal in the composition for forming a metal film.
From the viewpoint of being able to form a dense and uniform metal film, the metal content relative to the total amount of the metal film-forming composition is preferably in the range of 0.5 mass % to 10 mass %, and more preferably in the range of 1 mass % to 8 mass %.
When the metal content is within the above range, the structure of the metal film formed from the metal film-forming composition becomes more uniform, and the electrical conductivity and thermal conductivity become better.
The metal content in the metal film-forming composition can be measured, for example, by the method described in "Basics of Coordination Chemistry: Werner Complexes and Organometallic Complexes" (KS Chemistry Specialist Book: Kodansha, 1989).

(Step III)
Step III is a step of applying the metal film-forming composition obtained in step II to a substrate.
In the composition for forming a metal film obtained through the above-mentioned step II, the metal complex is present uniformly in a high concentration in an aqueous solvent, and due to the function of the coexisting organic reducing agent, the stability of the metal complex is good. Furthermore, the metal complex contained in the composition has good adsorption properties to the surface of a hard substrate, so that a metal film having a dense structure can be formed on the surface of any substrate.
That is, in step III, the metal film-forming composition is applied to any substrate, whereby the metal complex is adsorbed onto the substrate surface, forming a dense metal film.

For example, when copper is used as the metal, copper nanoparticles derived from a copper complex adhere to the substrate to form a copper film, and the copper film thus formed has excellent electrical conductivity and thermal conductivity.
In addition, when the metal complex contained in the metal film-forming composition has an ammonium group, a ligand derived from ethylenediamine, etc., the metal complex has good adhesion to inorganic substrates, particularly glass substrates, and therefore the metal film formed using the metal complex is expected to have excellent adhesion to inorganic substrates.

--Application of metal film-forming composition to substrate--
In step III, the obtained metal film-forming composition is applied to a substrate to form a metal film-forming composition layer. Since the metal complex contained in the metal film-forming composition in the present disclosure has good adsorption to the substrate, a dense metal film is formed on the substrate by removing the solvent from the metal film-forming composition layer.
There is no particular limitation on the method for applying the metal film-forming composition to the substrate in step III, and various methods such as known coating methods and immersion methods can be used depending on the material, shape, etc. of the substrate.
It is preferable that the process III of applying the metal film-forming composition to the substrate includes at least one of a process of applying the metal film-forming composition to the substrate, a process of immersing the substrate in the metal film-forming composition, and a method of storing the metal film-forming composition inside a container-shaped substrate.

Examples of methods for applying the metal film-forming composition to a substrate include spray coating, spin coating, blade coating, bar coating, roll coating, die coating, flow coating, etc. The metal film-forming composition may also be applied to a substrate by a casting method.
An appropriate coating method may be selected taking into consideration the physical properties such as the viscosity of the metal film-forming composition, the thickness of the metal film to be formed, and the like.
As a method for locally applying the metal film-forming composition to the substrate, a printing method such as screen printing, inkjet printing, etc. may be applied. By using the printing method, a metal film can be locally formed only in a desired region of the substrate.
Generally, the coating amount of the metal film-forming composition is preferably in the range of 1 μm to 10 μm, and more preferably in the range of 3 μm to 5 μm, in terms of wet film thickness.

When forming a metal film on one side of a substrate, it is preferable to apply a metal film-forming composition to one side of the substrate to form a coating film (composition layer for forming a metal film) of the composition for forming a metal film, and then leave it for a certain period of time, from the viewpoint of forming a denser film. The leaving time is preferably 6 hours or more, more preferably 12 hours or more, at room temperature (25°C), for example. By leaving the composition layer for forming a metal film formed on the substrate, the metal contained in the composition for forming a metal film is adsorbed to the substrate to form a metal film. There is no particular limit to the upper limit of the leaving time, but in consideration of productivity, it can be 120 hours or less, and 90 hours or less is preferable.
In addition, after applying the metal film-forming composition to one side of the substrate to form a metal film-forming composition layer, the composition is left to stand, and the atmospheric temperature of the region to be left to stand, the liquid temperature of the formed metal film-forming composition layer, etc. are set to room temperature or higher, for example, 30° C. or higher, preferably 40° C. or higher, thereby increasing the reaction rate and enabling a dense metal film to be formed in a shorter standing time. The temperature is preferably 80° C. or lower from the viewpoint of not affecting the metal film-forming composition.
For example, the standing time is preferably 4 hours or more, and more preferably 8 hours or more, when the atmospheric temperature is 35° C. The upper limit of the standing time is the same as that at room temperature.
After the metal film is formed, the remaining metal film-forming composition may be removed.

As a method for applying the metal film-forming composition, an immersion method in which the substrate is immersed in the metal film-forming composition, such as a dip method, may be used. The immersion method makes it possible to easily form a metal film on a substrate of any shape that has been molded, or to form a metal film on both sides of a flat substrate.

In the manufacturing method of the present disclosure, a metal film can be formed on the surface of a substrate by simply applying a metal film-forming composition to the substrate, i.e., by contacting the metal film-forming composition with the substrate surface. Therefore, by using a method in which the metal film-forming composition is stored inside a container-shaped base, a metal film can be formed only on the inner surface of the container-shaped substrate.
For example, when forming a metal film only on the inner surface of a glass tube shaped like a test tube with one end sealed, it is difficult to apply a coating method or a dipping method. However, according to the manufacturing method disclosed herein, a metal film can be easily formed only on the inside of a glass tube by injecting a metal film forming composition into a glass tube with one end sealed and storing the metal film forming composition in the glass tube.
By applying this method, a metal film can be easily formed only on the inner surface of a container-shaped substrate. Also, by injecting a metal film-forming composition into a hollow tube such as a cylindrical tube and sealing both ends, a metal film can be formed on the inner surface of any hollow tube.
When a metal film-forming composition is stored in a hollow tube, such as a glass tube sealed at one end, and left to stand for a period of time, a metal film is likely to be formed downward in the direction of gravity. For this reason, it is preferable from the viewpoint of forming a uniform metal film to rotate the hollow tube storing the metal film-forming composition at an angle of 90°, 180°, etc. in the circumferential direction with respect to the direction of gravity, for example, to arrange the longitudinal direction of the glass tube horizontally and periodically rotate the entire glass tube in the circumferential direction with respect to the central axis of the cylinder of the glass tube when the composition is left to stand for a period of time.

When the metal film-forming composition is applied to the substrate by at least one of the methods of immersing the substrate in the metal film-forming composition and storing the metal film-forming composition in a container-shaped substrate, the immersion time or storage time is, for example, preferably 6 hours or more at room temperature (25° C.), more preferably 12 hours or more. When it is desired to increase the film thickness, the immersion time or storage time can be 24 hours or more.
There is no particular upper limit to the immersion time or storage time, but from the viewpoint of productivity, it can be 120 hours or less, and preferably 90 hours or less.
By setting the atmospheric temperature of the region in which the metal film-forming composition is stored, the temperature of the metal film-forming composition, etc. to room temperature or higher, for example, 30° C. or higher, preferably 40° C. or higher, the reaction rate increases and a dense metal film can be formed inside the container-shaped substrate in a shorter storage time. The temperature is preferably 80° C. or lower from the viewpoint of not affecting the metal film-forming composition.
For example, when the atmospheric temperature is 35° C., the retention time is preferably 4 hours or more, and more preferably 8 hours or more. The upper limit of the retention time is the same as that at room temperature.

The thickness of the metal film formed on the substrate can be selected according to the purpose. In the case of a method in which a metal film is applied to a substrate, the thickness of the metal film can be controlled by the amount of the metal film-forming composition applied to the substrate, the composition of the metal film-forming composition, the contact time between the metal film-forming composition and the substrate (the time the metal film-forming composition layer is left standing), etc.

When applying the method of immersing the substrate in the metal film-forming composition or the method of storing the metal film-forming composition in a substrate having one end sealed, the thickness of the metal film can be controlled by controlling the composition of the metal film-forming composition, the contact time between the substrate and the metal film-forming composition, etc.

(Base material)
The substrate for forming the metal film can be appropriately selected depending on the purpose.
According to the manufacturing method of the present disclosure, a metal film can be formed on a substrate by simply applying a metal film-forming composition to the substrate. Therefore, according to the manufacturing method of the present disclosure, if the material is taken into consideration, a metal film can be formed on a substrate such as a non-conductive substrate or a substrate with low heat resistance. Also, if the shape of the substrate is taken into consideration, a metal film can be formed on a substrate of any shape, such as a substrate having a curved surface, a porous substrate, or the inside of a cylindrical substrate.
Therefore, depending on the intended use of the metal film, a substrate having various physical properties such as heat resistance, dimensional stability, solvent resistance, electrical insulation, processability, gas barrier properties, low moisture absorption, waterproofing, etc. can be arbitrarily selected and used. For example, a material generally used for a circuit board can be used as the substrate.
From the viewpoint of good dimensional stability, the substrate is preferably an inorganic substrate such as glass, ceramics, metal, etc. More specifically, examples of the inorganic substrate include glass substrates such as alkali-free glass substrates, soda glass substrates, Pyrex (registered trademark) glass substrates, and quartz glass substrates, semiconductor substrates such as silicon substrates, metal substrates such as stainless steel substrates, aluminum substrates, and zirconium substrates, and metal oxide substrates such as alumina substrates.

According to the manufacturing method of the present disclosure, since it is possible to form a metal film on a substrate without the need for heat treatment at 100° C. or higher, an organic substrate can also be suitably used. As the organic substrate, in addition to resin substrates such as thermosetting resins and engineering plastics having relatively high heat resistance, a metal film can be easily formed on an organic substrate containing a resin having relatively low heat resistance, for example, an organic substrate containing a certain type of thermoplastic resin and thermosetting resin.
Therefore, there is an advantage that a metal film can be easily formed on any surface of a molded body, for example, a molded body made of a thermosetting resin or a molded body made of a thermoplastic resin that has been molded in advance.
Examples of resins that can be used as the organic base material include resins having relatively good heat resistance, such as fluororesins such as tetrafluoroethylene, polyethylene terephthalate (PET), high density polyethylene, and polyimide.
Another example of a resin that can be used as the organic substrate is a thermoplastic resin or a thermosetting resin having at least one of the deflection temperature under load (hereinafter, simply referred to as "deflection temperature under load") specified in JIS K7191 (2015) and the continuous heat resistance temperature according to the long-term heat resistance continuous test (UL-746B (2013)) of less than 150°C. Furthermore, according to the manufacturing method of the present disclosure, a resin with relatively low heat resistance, such as a thermoplastic resin or a thermosetting resin having at least one of the deflection temperature under load and the continuous heat resistance temperature of less than 100°C, can also be used as the organic substrate.

The deflection temperature under load of an organic substrate is a physical property defined in JIS K7191 (2015), and in this disclosure, a value measured under a load of 1.81 MPa is used.
JIS K7191 (2015) is composed of a group of standards consisting of JIS K7191-1 Part 1: General rules, JIS K7191-2 Part 2: Plastics and ebonite, and JIS K7191-3 Part 3: High-strength thermosetting resin laminates and long-fiber reinforced plastics. The deflection temperature under load can be measured in accordance with any of these groups of standards depending on the resin.
UL-746B (2013), a long-term continuous heat resistance test for organic substrates, is a standard from Underwriters Laboratories Inc. and indicates the temperature at which the physical properties (strength) deteriorate to 50% of the initial value when left in the atmosphere at a certain temperature for a specified period of time, typically 40,000 hours, and serves as a guide to the heat resistance temperature at which a substrate can be used continuously without load.
When the resin applied to the organic substrate is a thermoplastic resin, the melting point of the resin can also be used as a guide to heat resistance.
The melting point of the resin can be measured by a known measurement method suitable for the resin, for example, JIS K7121 (1987) Plastic transition temperature measurement method (related standard: ASTM D3418-82). The softening point can be measured by the Vicat softening point measurement method described in JIS K7206 (2016).
Below, at least one of the deflection temperature under load (load of 1.81 MPa) and the continuous heat resistance temperature is described for examples of resin materials that can be used as the substrate. For thermoplastic resins, the melting point (literature value) is also described.
Examples of organic substrates in the metal film laminate of the present disclosure include the resins described in 5.4 Plastic Materials I-715 to I-717 of the Chemical Handbook, Basic Edition, Revised 5th Edition (Maruzen Publishing: 2004), and the deflection temperatures under load (loaded at 1.81 MPa) described in the relevant sections can be referenced. In Table 1 below, "-" indicates that the data is unknown or cannot be measured.

Resins that can be used for the resin substrate include polyethylenes such as PET, low-density polyethylene (LDPE), and high-density polyethylene (HDPE), polycarbonate (PC), polyvinyl chloride (PVC), polystyrene, and acrylic resins such as polymethyl methacrylate (PMMA), polyamides such as nylon 6, phenolic resins, melamine resins, and urethane resins.
The upper limit of heat resistance of rigid polyurethane foam is about 150° C., while the upper limit of heat resistance of flexible polyurethane foam is about 80° C., but according to the manufacturing method of the present disclosure, the porous polyurethane foam can be used as a substrate. That is, according to the manufacturing method of the present disclosure, it is possible to form a metal film on the surface of the polyurethane foam, including the inside of the pores.
Another feature of the manufacturing method of the present disclosure is that a high-purity metal film can be formed on an organic substrate having a relatively low heat resistance, that is, a melting point or softening point of less than 150°C, more preferably less than 100°C.

The substrate may have a single layer structure or a laminate structure using a plurality of different materials. A substrate having a modified metal may also be used. Examples of the substrate having a modified metal include an aluminum substrate having an oxide film formed by subjecting an aluminum substrate to an oxidation treatment, an yttrium-stabilized zirconium substrate, and a stainless steel substrate.
Furthermore, a metal film can be formed on the above-mentioned urethane foam, as well as on porous substrates such as ceramic porous plates and nonwoven fabrics.

The thickness of the substrate can be selected depending on the intended use.
Furthermore, according to the manufacturing method of the present disclosure, an existing member can be used as a substrate, and a metal film can be formed on any surface of the substrate.

In step III, as described above, a metal film can be formed simply by applying the metal film-forming composition to a substrate, so that a metal film can be formed on any surface of substrates of various shapes, not just flat substrates.

The method for producing a metal film according to the present disclosure may further include other steps in addition to steps I, II, and III. The other steps include drying the metal film-forming composition formed in step III, more specifically, drying the metal film-forming composition layer, and subjecting the formed metal film to a heat treatment (annealing (firing) treatment).

(Other processes)
--Step of drying the metal film-forming composition--
The manufacturing method of the present disclosure may further include a step of drying the metal film-forming composition applied to the substrate in step III.
The solvent contained in the metal film-forming composition is removed by drying, and a metal film is formed on the substrate.
The drying in the present disclosure includes natural drying at room temperature. Furthermore, by subjecting the metal film-forming composition to heat drying or the like as described below, a metal film that is in close contact with the substrate can be formed more quickly than in the case of natural drying.
The term "drying" used here refers to reducing the amount of solvent contained in the metal film-forming composition, and does not necessarily mean completely removing the solvent.

Drying can be carried out by a conventional method.
As the drying method, in addition to the above-mentioned natural drying, drying by heating, drying by blowing an air current, etc. can be used.
In the case of natural drying, the material may be left to stand at room temperature for 60 minutes to 5 hours.
In the case of drying by heating, a known heating means can be appropriately selected and used. Examples of the heating method include a method of contacting a heating means such as a plate heater or a heat roll from the back side of the substrate, a method of passing through a heating zone such as an electric furnace, a method of irradiating with energy rays such as infrared rays or microwaves, and a method of blowing hot air.
The heating temperature during the heat drying is not particularly limited. In consideration of drying efficiency and suppression of effects on the substrate, the heating temperature can be in the range of 30° C. or more and less than 100° C., and is preferably in the range of 30° C. to 60° C.
From the viewpoint of productivity, the drying time during heat drying is preferably within the range of 10 seconds to 20 minutes.

In the manufacturing method disclosed herein, the step III of applying the metal film-forming composition to the substrate and the step of drying the metal film-forming composition applied to the substrate can be performed multiple times.

First, in step III, a metal film-forming composition is applied to a substrate, and the metal film-forming composition is dried to form a metal film on the substrate. Then, when the metal film-forming composition is applied again to the substrate on which the metal film has been formed, the metal complex contained in the metal film-forming composition is adsorbed onto the surface of the metal film formed on the substrate. Then, by drying, a thicker metal film is formed.
The amount of the metal film-forming composition that can be applied to the substrate may be limited by the physical properties of the metal film-forming composition. However, regardless of the type of metal film-forming composition used, applying the metal film-forming composition and drying the composition multiple times can form a metal film that is thicker than the metal film obtained by applying the metal film-forming composition and drying the composition only once. Therefore, by controlling the number of times the above steps are repeated, a metal film of any thickness can be easily formed on the substrate.

When a metal film-forming composition is applied to a substrate on which a metal film has been formed, the metal film-forming composition comes into contact with the metal film already formed. The metal precursor contained in the metal film-forming composition adheres between the metal particles contained in the already formed metal film, causing the metal particles to grow, and metal precipitation is carried out quickly. As a result, the metal particles contained in the metal film are more densely packed, which is expected to not only improve the thickness of the metal film, but also improve the physical properties of the metal film, such as electrical conductivity.

--Process of heat treating the formed metal film--
According to the manufacturing method of the present disclosure, it is possible to form a metal film without the need for heat treatment at a temperature of 100° C. or higher.
However, depending on the purpose of the metal film and the type of base material used, a heat treatment step of further heating the formed metal film may be carried out.
The heating temperature can be 100° C. or higher. When the substrate is a heat-resistant substrate such as a metal, ceramic, or engineering plastic, the heat treatment can be performed at 200° C. to 500° C., which is a temperature generally used for annealing a metal film.
By carrying out the heat treatment step, further effects may be achieved, such as the metal nanoparticles derived from the metal complex present on the substrate being fused to each other, the remaining metal complex being rapidly converted to metal, and the solvent being more rapidly removed, and it is expected that the structure of the metal film formed on the substrate will become denser.

The heating conditions are appropriately selected depending on the purpose of the metal film and the properties of the metal contained in the metal film-forming composition.
For example, when the complex contains a metal atom selected from the group consisting of Cu, Li, Ni, Mn, Zn, and Co, the heating treatment can be performed at a temperature of 100° C. or higher. From the viewpoint of making the effect of the heat treatment more pronounced, it is preferable to perform the heat treatment at a temperature of 200° C. or higher, and more preferably at a temperature of 250° C. or higher.
There is no particular upper limit to the heating temperature, and it may be appropriately selected depending on the physical properties of the metal, such as the melting point and softening point, and the heat resistance of the substrate to be used. In general, the heating temperature may be 500° C. or less. If the metal film is heated at a temperature exceeding 500° C., the effect of forming the metal film will not be further improved, and may instead affect the substrate.

When the heat treatment step is performed, the heating may be performed in an air atmosphere or in an inert gas atmosphere. When the heating is performed in an atmosphere containing an inert gas, examples of the inert gas include nitrogen gas, helium gas, and argon gas.
When the heat treatment is carried out in an atmosphere that reduces the oxygen concentration, such as an inert gas atmosphere, the oxygen concentration is preferably 10 ppm or less.
From the viewpoint of uniformity of the metal film to be formed, it is also preferable to heat the metal film by raising the temperature to a heating temperature selected depending on the type of metal and then maintaining the heating temperature for several minutes.
As described above, when forming a thicker metal film, in addition to the step of applying the metal film-forming composition to the substrate and the step of drying, a heating treatment step may be carried out, and these three steps may be carried out multiple times.

As one embodiment of the heating step, the formed metal film is annealed (fired) at a temperature of 200°C to 500°C.
The uniformity of the formed metal film can be further improved by further heating the formed metal film through an annealing (firing) process. The firing temperature during the annealing process is preferably 200° C. to 500° C., and more preferably 300° C. to 500° C.

(Metal Film)
The thickness of the metal film obtained by the manufacturing method of the present disclosure is selected according to the purpose. Since the metal film-forming composition of the present disclosure contains a metal complex derived from a specific metal compound uniformly in a dissolved state, it is possible to form an extremely thin metal film, for example, 10 nm to 200 nm.
Furthermore, by applying a method in which the application of the metal film-forming composition and the drying of the metal film-forming composition are repeated multiple times, it is possible to easily form a thicker metal film, specifically a metal film having a thickness on the order of several microns.
The thickness of the metal film formed by applying the above-mentioned metal film-forming composition once is preferably 50 nm to 150 nm.
The thickness of the obtained metal film can be measured by a known measurement method by observing a cross section of the metal film formed on the substrate with a scanning electron microscope or the like as described in detail in the Examples.

The metal film obtained by the manufacturing method of the present disclosure contains only a specific metal compound as a metal material in the metal film forming composition as a raw material, and therefore, a metal film having a dense structure and high purity can be formed. Therefore, for example, when copper is used as the metal, the formed copper film has a dense structure and is excellent in electrical conductivity and thermal conductivity.
When a metal film is formed using a metal film-forming composition that contains only a specific metal compound having a single metal, the content of the metal in the formed metal film is preferably 90 mass % or more, and more preferably 95 mass % or more.

The metal film obtained by the manufacturing method of the present disclosure is a high-purity metal film due to the manufacturing method. According to the manufacturing method of the present disclosure, a metal film is formed on a substrate without the need to contain a catalyst, as in the case of an electroless plating solution. The raw metal of the metal film obtained by the manufacturing method of the present disclosure is only the specific metal compound contained in the metal film forming composition, so the obtained metal film does not contain any other metal than the metal contained in the specific metal compound.
Therefore, the manufacturing method of the present disclosure is preferably a manufacturing method for obtaining a metal film in which the content of a metal other than the metal contained in the specific metal compound is below the detection limit in analysis by X-ray diffraction.
The content of the target metal in the metal film can be measured, for example, by X-ray diffraction (XRD). The method for measuring the metal content in the metal film by X-ray diffraction will be described in the Examples.

The metal film obtained from the metal film-forming composition contains an extremely small amount of impurities.
Although slight impurities derived from the solvent may remain in the metal film, they are mainly carbon atoms derived from the solvent, and there is no concern that they will impair the properties of the formed metal film. This is a major advantage compared to electroless plating films that require reducing agents, and metal films formed by precursor methods using anionic metal complexes.

According to the manufacturing method of the present disclosure, a metal film can be formed uniformly over the entire surface of any surface of any substrate, and can also be formed in a pattern. Also, a metal film can be formed only on the inner surface of a container-shaped substrate.
In addition, when forming a patterned metal film, the metal film-forming composition can be applied to a substrate in an arbitrary pattern by using a printing method as described above to form a patterned metal film. As a method for forming a patterned metal film, a method of forming a uniform metal film on a substrate and then patterning the film using a known method such as etching to form a patterned metal film can be further mentioned.

The manufacturing method of the present disclosure can also be applied to the formation of a metal oxide film containing the metal.
Methods for forming a metal oxide film by applying the manufacturing method of the present disclosure include a method in which a metal film formed from a metal film-forming composition is further heat-treated to form an oxide film, and a method in which an oxidizing atmosphere is actively created when a metal film is formed using a metal film-forming composition, and heat treatment is performed under an oxidizing atmosphere.
Examples of the method for producing a metal oxide film by heat-treating the formed metal film in an oxidizing atmosphere include a method in which the atmosphere in which the metal film is placed has an oxygen concentration of 5% to 80%, and the heat treatment is performed at a temperature of 200° C. or higher for 0.5 hours or more. There is no particular limit to the upper limit of the heat treatment temperature and the heat treatment time. For example, it is expected that the longer the heat treatment time, the more the oxidation of the metal film will progress. The upper limit of the heat treatment temperature may be limited by the heat resistance of the substrate. For example, when a metal substrate, a ceramic substrate, or the like is used, the heat treatment temperature can be set to 1000° C. or lower in terms of manufacturing suitability.
The upper limit of the heat treatment time is appropriately selected depending on the properties of the desired metal oxide film, the characteristics of the substrate used, etc. From the viewpoint of production suitability, the upper limit of the heat treatment time can be, for example, 96 hours or less.

The manufacturing method disclosed herein can easily form a dense metal film that has excellent adhesion to the substrate, making it suitable for fields that require metal films, particularly thin copper films. In addition, because there is a high degree of freedom in the selection of substrate types and metal types, the manufacturing method disclosed herein can be applied to a variety of fields.

<Metal Film Forming Composition>
The metal film-forming composition of the present disclosure comprises a metal precursor liquid containing a reaction product of at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine, and an organic reducing agent, and the content of metal ions contained in the metal precursor liquid per 100 parts by mass of the organic reducing agent is in the range of 50 parts by mass to 400 parts by mass.
The metal film-forming composition of the present disclosure is suitably used in the above-described method for producing a metal film of the present disclosure.
The metal precursor liquid and the organic reducing agent contained in the metal film-forming composition of the present disclosure are the same as the metal precursor liquid and the specific reducing agent described in the production method of the present disclosure above, and preferred examples are also the same.

In the metal film forming composition of the present disclosure, the metal ions contained in the metal precursor liquid are in the range of 50 to 400 parts by mass per 100 parts by mass of the specific reducing agent. From the viewpoint of improving the metal film forming properties of the metal film forming composition, it is preferable that the metal ions contained in the metal precursor liquid are in the range of 100 to 350 parts by mass per 100 parts by mass of the specific reducing agent, and it is more preferable that the metal ions contained in the metal precursor liquid are in the range of 150 to 350 parts by mass per 100 parts by mass of the specific reducing agent.

It is believed that when the content of the metal ion is 50 parts by mass to 400 parts by mass per 100 parts by mass of the specific reducing agent, the reducibility of the metal ion contained in the metal complex is further improved, and the precipitation of the metal is maintained at an appropriate rate due to the reduction of the metal ion attached to the substrate, so that a dense metal film is formed on the substrate.
If the content of metal ions relative to 100 parts by mass of the specific reducing agent is less than 50 parts by mass, the rate at which the specific metal compound is reduced will decrease, raising concerns that the metal film will not be formed efficiently. If the content of metal ions relative to 100 parts by mass of the specific reducing agent exceeds 400 parts by mass, the rate at which the metal is precipitated due to the reduction of the metal ions will increase further, raising concerns that the formed metal film will be peeled off and that metal particles will be precipitated that cannot adhere to the substrate.

The content of metal ions in the metal film-forming composition can be measured, for example, by the method described in "Basics of Coordination Chemistry: Werner Complexes and Organometallic Complexes" (KS Chemistry Specialist Book: Kodansha, 1989).
The content of the specific reducing agent in the metal film-forming composition can be measured, for example, by the following method.
First, the metal film-forming composition is dried to prepare a powder. The obtained powder is analyzed using a thermogravimeter-differential thermal analyzer (TG-DTA) to measure the content of the specific reducing agent.
In the present disclosure, the thermogravimetric differential thermal analyzer used is a TG-DTA2000S (product name) manufactured by Mac Science, Inc., and the values used are those measured at a temperature increase rate of 10° C./min while ventilating 100 ml (milliliters)/min of air.

The pH of the metal film-forming composition of the present disclosure at room temperature (25° C.) is preferably 6 to 8, and more preferably a neutral range near pH 7.5.
The pH of the metal film-forming composition can be measured with a known pH meter.

The metal film forming composition of the present disclosure contains a specific reducing agent, which is an organic component, and contains only metal ions as metal components that contribute to the formation of the desired metal film, and does not need to contain other metal components, such as reducing metals used in displacement plating or catalysts used in electroless plating. Therefore, the metal film formed by the metal film forming composition of the present disclosure does not contain catalysts, etc., and is a high-purity, dense metal film.

The metal film-forming composition of the present disclosure can be brought into contact with any substrate to form a metal film on the substrate without the need for heat treatment at 100°C or higher, and therefore can form an electrically conductive metal film at any position, even on substrates with low heat resistance or substrates that are not flat molded bodies. In addition, by controlling the formulation of the metal film-forming composition, the contact time between the substrate and the metal film-forming composition, the number of contacts, etc., a metal film of any thickness can be formed, and therefore the range of applications is wide.

<Metal Film Laminate>
The metal film laminate of the present disclosure is a metal film laminate having, on the non-conductive substrate, a metal film which is a cured product of a metal film-forming composition which comprises a metal precursor liquid containing a reaction product of at least one selected from the group consisting of metal complexes and metal salts with at least one selected from ammonia and an amine, and at least one organic reducing agent selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid, wherein the content of metal ions contained in the metal precursor liquid per 100 parts by mass of the organic reducing agent is in the range of 50 parts by mass to 400 parts by mass.
The metal film laminate of the present disclosure can be obtained by the manufacturing method of the present disclosure described above.

The metal film on the non-conductive substrate is preferably a metal film in which the content of a metal other than the specific metal compound is below the detection limit in analysis by X-ray diffraction.
There is no particular limit to the thickness of the metal film, and it can be appropriately selected according to the purpose. The thickness of the metal film can be 10 nm or more. There is no particular limit to the upper limit, and as necessary, for example, the film may have a thickness of 3 μm or more, preferably 5 μm or more. From the viewpoint of manufacturability, the film thickness can be 10 μm or less.
For example, when obtaining a metal film laminate by applying the manufacturing method of the present disclosure described above, a metal film having a larger thickness can be easily formed by applying the metal film-forming composition of the present disclosure onto a substrate and repeating the drying process multiple times.

The thickness of the metal film in the metal film laminate is preferably 20 nm or more, more preferably 50 nm or more, for example, when the metal film laminate has an electrically conductive function and has a metal film on a substrate. When the metal film is used as wiring, the thickness of the metal film is preferably 3 μm or more, more preferably 5 μm or more. There is no particular limit to the upper limit of the metal film in the electrically conductive metal film laminate. The thickness of the metal film can be, for example, 10 μm or less from the viewpoint of productivity.
When a metal film laminate having a copper film, a silver film or the like as the metal film is used as the antibacterial material, the thickness of the metal film is preferably 1 μm to 5 μm, and more preferably 2 μm to 4 μm, from the viewpoint of a good balance between antibacterial effect and usability.
The thicknesses of the non-conductive substrate and the metal film in the metal film laminate can be measured by the method already described.

There are no particular limitations on the non-conductive substrate, and it can be arbitrarily selected from glass substrates, ceramic substrates, thermoplastic resin substrates, thermosetting resin substrates, and the like.
The metal film in the metal film laminate of the present disclosure is a cured product of the metal film-forming composition of the present disclosure, and is a metal film that is formed by contacting the metal film-forming composition with a substrate and drying it, without the need for heating.
Therefore, the metal film laminate of the present disclosure can also take the form of a laminate having a dense metal film on a substrate containing a resin having at least one of a deflection temperature under load and a continuous heat resistance temperature of less than 150°C.

Examples of resins that can be used as the non-conductive substrate include resins with good heat resistance, such as fluororesins such as tetrafluoroethylene, polyethylene terephthalate, and high density polyethylene.
Furthermore, as exemplified in the section on the manufacturing method of the present disclosure, an organic substrate such as a thermoplastic resin or a thermosetting resin having at least one of a deflection temperature under load and a continuous heat resistance temperature of less than 150° C., and further less than 100° C., can also be used as the non-conductive substrate.
Examples of the thermoplastic resin and the thermosetting resin having at least one of the deflection temperature under load and the continuous heat resistance temperature of less than 150° C. include the resins exemplified in the section on the manufacturing method of the present disclosure described above, and preferred examples are also the same.

Thermoplastic resins having a melting point or softening point of less than 150° C. have good moldability, and a molded body of an organic substrate having any shape can be easily obtained by a known method. By forming the obtained molded body of the thermoplastic resin as the organic substrate into the metal film laminate of the present disclosure, a metal film laminate having a substrate and a metal film having any shape can be easily obtained.
It is also possible to provide a metal film laminate having an organic substrate having a relatively low heat resistance, such as the above-mentioned urethane foam.

The metal film in the metal film laminate of the present disclosure has good adhesion to the substrate.For example, by using the same manufacturing method as that described in Example 1 below, a metal film laminate having a copper film with a thickness of 5 μm on a glass substrate is obtained, and even when a peel test between the substrate and the metal film is performed using the JIS H 8504 (1999) peel test method, it is confirmed that the metal film laminate has a film with good adhesion and does not show peeling or swelling.
The metal film laminate of the present disclosure can be a metal film laminate having a metal film and a non-conductive substrate of various shapes, such as not only a flat plate-like shape but also a substrate having a curved surface or a porous substrate, and has a wide range of applications.

The manufacturing method of the present disclosure, the metal film forming composition used in the manufacturing method of the present disclosure, and the metal film laminate obtained by the manufacturing method of the present disclosure will be specifically described below with reference to examples. However, the present disclosure is not limited to the following examples, and can be practiced in various modified examples as long as it does not deviate from the gist of the disclosure.

Example 1
(1. Preparation of an aqueous solution of copper complex)
2.54 g of copper formate tetrahydrate, which is a metal salt, and 4.56 g of 25% by mass ammonia water were added to 25 g of pure water, and the mixture was stirred at room temperature at 500 rpm for 1 hour to obtain a metal precursor liquid. The obtained metal precursor solution was deep blue when visually observed. (Step I)

(2. Preparation of Aqueous Ascorbic Acid Solution)
72 g of pure water and 18 g of ascorbic acid as an organic reducing agent were mixed and stirred at a liquid temperature of 40° C. for 10 minutes to obtain a colorless and transparent aqueous solution of ascorbic acid.

(3. Preparation of Metal Film-Forming Composition)
The metal precursor liquid obtained in (1) and the ascorbic acid aqueous solution obtained in (2) were mixed in a ratio of 100 parts by mass of ascorbic acid to 300 parts by mass of copper in the metal precursor solution, and the mixture was stirred at room temperature for 20 minutes to obtain a composition for forming a metal film. (Step II)
Immediately after mixing the metal precursor liquid obtained in (1.) and the aqueous ascorbic acid solution obtained in (2.), the mixture was deep green in color. However, when mixing was continued, after 20 minutes the obtained composition for forming a metal film changed to yellow.
The pH of the metal film-forming composition obtained in Example 1 was measured using a pH meter (PICCOLO+, manufactured by HANNA Instruments), and the pH of the metal film-forming composition at 25° C. was 7.5.
In addition, when the amount of metal (copper) ions and the amount of ascorbic acid, which is an organic reducing agent, contained in the composition for forming a metal film were measured using the method described above, the content of copper ions per 100 parts by mass of ascorbic acid was found to be 300 parts by mass.

(4. Application of metal film-forming composition to substrate)
Four thoroughly cleaned quartz glass plates (length: 20 mm x width: 20 mm x thickness: 1.5 mm) were placed in a polystyrene plastic petri dish (diameter 90 mm, depth 15 mm).
30 g of the composition for forming a metal film obtained in step II was poured into a plastic petri dish, and a quartz glass plate was immersed in the composition for forming a metal film and allowed to stand at room temperature for 3 days.
After three days, the quartz glass plate was removed from the plastic petri dish, washed five times with pure water, and then dried at room temperature to obtain a quartz glass plate (hereinafter referred to as laminate 1) having a copper film formed on the surface of the quartz glass plate by the manufacturing method of Example 1. (Step III)

Example 2
The laminate 1 (quartz glass plate on which a copper film was formed) obtained in Example 1 was placed in a plastic petri dish, and 30 g of the metal film-forming composition obtained in the same manner as in step II of Example 1 was poured into it. The laminate 1 was immersed in the metal film-forming composition and allowed to stand at room temperature for 3 days.
After three days, the laminate 1 was removed from the plastic dish, washed five times with pure water, and then dried at room temperature. By the manufacturing method of Example 2, a laminate 2 was obtained in which an additional copper film was formed on the surface of the copper film in the laminate 1 obtained in Example 1.

[Evaluation of copper film]
(1. Component Analysis)
X-ray diffraction (XRD) was measured for the copper films obtained in Examples 1 and 2 using a SMART Lab device (RIGAKU Corporation) with a parallel beam optical system having an incident angle of 0.3°, by measuring the intensity at a fixed time of 5°/min from 2θ of 10° to 80° in 0.05° steps.
The obtained XRD pattern is shown in Figure 2. As is clear from Figure 2, it was confirmed that the films obtained in Examples 1 and 2 were both single-phase copper. Moreover, in Example 2, in which the application of the metal film-forming composition and drying were repeated twice, it is presumed that a denser copper film with higher pattern strength was formed compared to Example 1.

(2. Copper Film Thickness)
The quartz glass plate on which the copper film was formed was cut perpendicularly to the surface direction, and the cut surface was photographed at a magnification of 5000 times using a scanning electron microscope (FE-SEM: JSM-6701F: product name, JEOL Ltd.) to obtain an FE-SEM image. Fig. 3(A) is an FE-SEM image of the cross section of the copper film in the laminate 1 obtained in Example 1, and Fig. 3(B) is an FE-SEM image of the cross section of the copper film in the laminate 2 obtained in Example 2.
From the cross-sectional FE-SEM images of FIG. 3, the thickness of the copper film was measured at three points, and the average thickness of the copper film was obtained by arithmetically averaging.
As a result, the average thickness of the copper film obtained in Example 1 was 4.29 μm, and the average thickness of the copper film obtained in Example 2 was 9.64 μm.

(3. Appearance Evaluation of Copper Film)
For laminate 1 and laminate 2, which are quartz glass plates on which a copper film is formed, FE-SEM images for film thickness measurement were taken under the same conditions from the surface direction on which the copper film was formed, to obtain FE-SEM images. Fig. 4(A) is an FE-SEM image of the copper film-formed surface of laminate 1 obtained in Example 1, and Fig. 4(B) is an FE-SEM image of the copper film-formed surface of laminate 2 obtained in Example 2.
The FE-SEM image in Figure 4 was observed, and the diameters of three copper nanoparticles randomly selected within the viewing angle were measured, and the arithmetic average was taken as the average particle diameter of the copper nanoparticles. Note that the longest diameter of the copper nanoparticles was taken as the particle diameter.
As a result, the average particle size of the copper nanoparticles in the copper film obtained in Example 1 was 3.5 μm, and the average particle size of the copper nanoparticles in the copper film obtained in Example 2 was 1.8 μm.

(4. Electrical Conductivity Evaluation)
The electrical conductivity of the copper films in the obtained laminates 1 and 2 was measured by the following method. The electrical resistance of the copper film was measured at five points by the four-probe method, and the average value of the three points excluding the maximum and minimum values of the measured values was calculated to be the electrical resistance value of the copper film (hereinafter, sometimes referred to as "resistance value"). The lower the resistance value, the better the electrical conductivity is evaluated to be.
The measurements were performed using a digital multimeter: Iwasaki Electric Co., Ltd. (formerly Iwatsu Measurement Co., Ltd.), VOAC7512, and KEITHLEY, Model 2010 Multimeter.
As a result, the electrical conductivity of the copper film in the laminate 1 obtained in Example 1 was 5.3×10 ⁻⁴ Ωcm, and the electrical conductivity of the copper film in the laminate 2 obtained in Example 2 was 1.8×10 ⁻⁴ Ωcm. From this, both of the obtained copper films showed sufficient electrical conductivity for practical use, despite being thin.

From the cross-sectional FE-SEM image of FIG. 3, the FE-SEM image of the copper film-formed surface of FIG. 4, and the evaluation of electrical conductivity, it was confirmed that, in the laminate 2 obtained in Example 2 in which the application of the metal film-forming composition and drying were repeated twice, the formed copper film was thicker, the size of the copper nanoparticles forming the copper film was smaller, and the electrical conductivity was improved, compared to the laminate 1 obtained in Example 1.
This is believed to be because by repeatedly applying the metal film-forming composition and drying it multiple times, the metal precursor comes into contact with the already formed metal film, adheres to between the metal particles in the metal film, and the metal particles grow, resulting in rapid precipitation of the metal, making the metal film denser, and improving the electrical conductivity.

Example 3
(1. Cleaning of glass tubes)
Using the metal film-forming composition obtained in Example 1, a copper film was formed on the inner surface of a glass tube (diameter: 12.75 mm, height: 100 mm) sealed at one end by the following procedure.
First, a glass tube with one end sealed was placed upright in a 500 ml (milliliter) beaker, and the glass tube was filled with Clean Ace (AS ONE Corporation) as a cleaning agent. Water was poured into the beaker, and ultrasonic waves were irradiated for 60 minutes (irradiation conditions: 70 W, 42 kHz). After that, the cleaning agent was discharged, and the inside of the glass tube was washed with pure water 10 times.
After that, the glass tube and the beaker were filled with pure water and ultrasonic waves were applied for 60 minutes. After the above treatment, the glass tube was dried for 60 minutes in a dryer at 70° C. to obtain a glass tube with one end sealed for forming a copper film.

(2. Application of Metal Film-Forming Composition to Glass Tube (Substrate))
The composition for forming a metal film obtained in Example 1 was poured into the washed and dried glass tube with one end sealed, and 12 g of the composition for forming a metal film was stored in the glass tube, and the opening of the glass tube was covered with parafilm in an upright state and allowed to stand at room temperature for 3 days. After being allowed to stand for 3 days, the composition for forming a metal film was discharged and naturally dried at room temperature for 24 hours.
Visual observation confirmed that a copper film having a metallic luster was formed on the inner surface of the glass tube.
FIG. 5 is a schematic cross-sectional view showing a copper film formed in a one-end sealed glass tube by the manufacturing method of Example 3, and a measurement terminal attached to the copper film for measuring the internal resistance of the copper film.
As shown in Fig. 5, a copper film 32 was formed inside a glass tube 30 sealed at one end by the manufacturing method of Example 3. The internal resistance of the formed copper film 32 was measured by a resistance meter by applying a pair of measuring terminals 34 located at the tips of a pair of conductors 36 connected to a resistance meter (not shown) to two points near the opening of the glass tube 30 sealed at one end with the copper film 32 formed therein, as shown in Fig. 5. As a result, the internal resistance of the formed copper film was 3 kΩ to 20 kΩ, and it was found that a copper film having electrical conductivity was formed.

(3. Reapplication of the metal film-forming composition to the glass tube (substrate))
Into the glass tube with one end sealed and a copper film formed on the inner surface, 12 g of the composition for forming a metal film obtained in Example 1 was poured and stored in the glass tube. The opening of the glass tube was covered with parafilm and allowed to stand at room temperature for 3 days. After being left standing for 3 days, the composition for forming a metal film was discharged and naturally dried at room temperature for 24 hours.
As a result, the copper film formed by applying the metal film-forming composition again had a higher metallic luster than the copper film formed after applying the metal film-forming composition only once.
The resistance value of the copper film formed inside the glass tube was measured in the same manner as described above, using the method shown in Fig. 5. The internal resistance value of the copper film obtained by the measurement was 0.3Ω to 1 kΩ, and it was confirmed that by applying the metal film-forming composition and drying it twice, a copper film with improved electrical conductivity was formed compared to a copper film formed by applying the metal film-forming composition and drying it only once.

From the evaluation results of the copper films produced in Examples 1 to 3, it was confirmed that a copper film having electrical conductivity can be easily formed on a substrate by simply applying a metal film-forming composition to the substrate and drying it.
It is also clear that by applying the metal film-forming composition to the substrate and drying it twice, a copper film can be formed that is denser, has a thicker film thickness, and has better electrical conductivity than when this is done only once.

Example 4
(1. Preparation of Electrolyte A)
A 500 mL (milliliter) Erlenmeyer flask was charged with 300 g of water, and while stirring, H ₄ EDTA (9.174 g: 31.39 mmol) and ammonia (4.773 g: 78.48 mmol) were added in that order. Stirring was continued at room temperature (25° C.) for 1 hour to obtain electrolyte solution A.
When the obtained electrolyte solution A was visually observed, it was found to be a transparent homogeneous solution.

2. Preparation of Metal Precursor Solutions
As shown in Fig. 1, two quartz cells (width: 100 mm x length: 100 mm x depth: 60 mm) were prepared as a pair of electrolyte tanks 16 and 18. The pair of electrolyte tanks 16 and 18 were connected by a flow path equipped with a cellulose dialysis filter (Visking Tube, manufactured by Nippon Medical Science Co., Ltd.) 12.
Thereafter, 150 g of the electrolyte A (electrolyte 20) obtained above was stored in each of the electrolyte tanks 16 and 18.
Next, electrodes 22, 24 were placed in the pair of electrolyte tanks 16, 18, respectively, so as to be in contact with the stored electrolyte A.
The electrodes 22 and 24 were made of copper plates (length: 900 mm x width: 37 mm x thickness: 0.3 mm).
The electrodes 22 and 24 were connected to a DC power source 26, and a voltage exceeding 0 V and up to 18 V was applied to supply a current of 2 A. As the power source, a DC stabilized power source (PMC18-2 (product name), Kikusui Electronics Co., Ltd.) was used.
By applying a voltage, in the electrolyte tank 16 in which the electrode 22 serving as an anode was placed, the electrolyte turned blue due to copper ions eluted from the copper plate serving as the electrode 22, and it was confirmed that a metal precursor liquid containing a copper complex was obtained (Step I).
On the other hand, no discoloration of the electrolyte was observed in the electrolyte tank 18 on the side where the electrode (copper plate) 24 serving as the cathode was placed. Also, it was confirmed that gas was generated from the electrode 24 serving as the cathode. When the gas was collected and examined, it was found to be hydrogen gas.

(3. Preparation of Metal Film-Forming Composition)
The metal precursor liquid obtained in step I and the 15 mass% aqueous solution of ascorbic acid prepared in Example 1 were mixed in a ratio such that the copper content in the metal precursor solution was 300 mass parts per 100 mass parts of ascorbic acid, and the mixture was stirred at room temperature for 20 minutes to obtain a composition for forming a metal film. (Step II)
Immediately after mixing the metal precursor liquid and the aqueous ascorbic acid solution obtained in Example 1, the mixed liquid was deep green in color. However, when mixing was continued, after 20 minutes the obtained composition for forming a metal film changed to yellow.

(4. Formation of Metal Film)
Four thoroughly cleaned quartz glass plates (length: 20 mm x width: 20 mm x thickness: 1.5 mm) were placed in a polystyrene plastic petri dish (diameter 90 mm, depth 15 mm).
30 g of the metal film-forming composition obtained in step II of Example 4 was poured into a plastic petri dish, and a quartz glass plate was immersed in the metal film-forming composition and allowed to stand at room temperature for 3 days.
After three days, the quartz glass plate was removed from the plastic petri dish, washed five times with pure water, and then dried at room temperature to obtain a quartz glass plate having a copper film formed on its surface by the manufacturing method of Example 4. (Step III)

(Evaluation of copper film)
The obtained copper film was evaluated in the same manner as in Example 1.
The copper film thus obtained was measured by X-ray diffraction (XRD), and the XRD pattern thus obtained confirmed that the copper film thus formed was a single phase of copper.

The resistance value of the obtained copper film was measured in the same manner as in Example 1.
As a result, the resistance value was 5.3×10 ⁻⁴ Ωcm, and the obtained copper film, although thin, exhibited sufficient electrical conductivity for practical use.

[Example 5-1, Example 5-2, Comparative Example 1]
(1. Preparation of an aqueous solution of copper complex)
To 35 g of pure water, 5.78 g of copper formate tetrahydrate (metal salt) and 10.48 g of 25% by mass aqueous ammonia were added, and the mixture was stirred at room temperature and 500 rpm for 1 hour to obtain a mixture.
Pure water was further added to adjust the copper ion concentration in the mixture to 0.5 mmol/g, thereby obtaining metal precursor liquid 2. (Step I)

(2. Preparation of Aqueous Ascorbic Acid Solution)
32 g of pure water and 8 g of ascorbic acid as an organic reducing agent were mixed and stirred for 30 minutes under conditions of room temperature (25° C.) and 500 rpm, and then further pure water was added to obtain a colorless and transparent aqueous ascorbic acid solution 2 having an ascorbic acid concentration of 1.14 mmol/g.

(3. Preparation of Metal Film-Forming Composition)
The metal precursor liquid 2 obtained in (1.) and the ascorbic acid aqueous solution 2 obtained in (2.) were mixed and stirred for 20 minutes at room temperature at 500 rpm to obtain a metal film-forming composition (i) of Example 5-1 in which the copper ion content per 100 parts by mass of ascorbic acid was 100 parts by mass. Similarly, by changing the mixing ratio, a metal film-forming composition (ii) of Example 5-2 in which the copper ion content per 100 parts by mass of ascorbic acid was 300 parts by mass was obtained. (Step II)
The amount of metal (copper) ions and the amount of ascorbic acid, which is an organic reducing agent, contained in each metal film-forming composition were measured by the methods described above.
In addition, a composition for forming a metal film of Comparative Example 1 was obtained in the same manner as for the composition for forming a metal film (i), except that the ascorbic acid aqueous solution 2 was not added to the metal precursor liquid 2 and 19.2 g of pure water was added.

(4. Application of metal film-forming composition to substrate)
Four thoroughly cleaned quartz glass plates (length: 20 mm x width: 20 mm x thickness: 1.5 mm) were placed in a polystyrene plastic petri dish (diameter 90 mm, depth 15 mm).
30 g of each of the compositions for forming a metal film obtained in step II was poured into a plastic petri dish, and a quartz glass plate was immersed in the composition for forming a metal film and allowed to stand at room temperature for 3 days.
After three days, the quartz glass plate was removed from the plastic dish, washed five times with pure water, and then dried at room temperature. When the metal film-forming compositions obtained in Examples 5-1 and 5-2 were used, a copper film was formed on the surface of the quartz glass plate.
When the comparative metal film-forming composition of Comparative Example 1 was used, no copper film was formed on the surface of the quartz glass plate. (Step III)

(5. Evaluation of Metal Film)
The resistance value of the obtained copper film was measured by the following method.
For the copper film formed on the glass plate, five randomly selected points on the film were measured by the two-terminal measurement method, and the average value of the three points excluding the maximum and minimum values was taken as the resistance value. The measurement was performed at room temperature using a two-terminal resistance meter (SANWA Digital Multimeter PC20, Sanwa Electric Instruments Co., Ltd.). The lower the resistance value measured by the above method, the better the electrical conductivity is evaluated to be.
As a result, the resistance value of the copper film obtained in Example 5-1 was 100 kΩ to 2 MΩ, and the resistance value of the copper film obtained in Example 5-2 was 1.3 Ω. All of the obtained copper films showed sufficient electrical conductivity for practical use.
On the other hand, in Comparative Example 1 in which a metal film-forming composition not containing ascorbic acid was used, no copper film was formed.

[Examples 6-1 to 6-4]
(1. Preparation of an aqueous solution of copper complex)
3.71 g of copper formate tetrahydrate, which is a metal salt, and 6.51 g of 25% by mass ammonia water were added to 45 g of pure water, and the mixture was stirred at room temperature at 500 rpm for 1 hour to obtain a metal precursor liquid. The obtained metal precursor solution was deep blue when observed visually. The copper ion concentration in the metal precursor liquid was adjusted to 0.3 mmol%. (Step I)

(2. Preparation of Aqueous Ascorbic Acid Solution)
35 g of pure water and 8.75 g of ascorbic acid as an organic reducing agent were mixed and stirred at room temperature for 30 minutes to obtain a colorless and transparent aqueous solution of ascorbic acid. The concentration of ascorbic acid in the aqueous solution was adjusted to 20% by mass.

(3. Preparation of Metal Film-Forming Composition)
The metal precursor liquid obtained in (1.) and the aqueous ascorbic acid solution obtained in (2.) were mixed in amounts such that the copper ion content in the metal precursor solution was 200 parts by mass (Example 6-1: composition (a) for forming a metal film), 300 parts by mass (Example 6-2: composition (b) for forming a metal film), 350 parts by mass (Example 6-3: composition (c) for forming a metal film), and 400 parts by mass (Example 6-4: composition (d) for forming a metal film) relative to 100 parts by mass of ascorbic acid, as shown in Table 2 below, and the mixture was stirred at room temperature for 20 minutes to obtain compositions (a) to (d) for forming a metal film. (Step II)

(4. Cleaning of Glass Tubes)
Using the metal film-forming composition 1 obtained in Example 1, a copper film was formed on the inner surface of a glass tube (diameter: 12.75 mm, height: 350 mm) sealed at one end by the following procedure.
First, a glass tube with one end sealed was placed upright in a 500 ml (milliliter) beaker, Clean Ace (AS ONE Corporation) was placed in the glass tube as a cleaning agent, and the glass tube was brushed for 2 minutes using a cleaning brush (brush scale: 22 mmΦ×180 mm). The inside of the glass tube was then washed with water 10 times. Next, 10 g of Clean Ace was placed in the glass tube and brushed for 1 minute. The glass tube was then washed with water 10 times, and the water was replaced with purified water 5 times and ethanol 3 times.
Thereafter, the glass tube was left to stand overnight at room temperature with the opening facing downwards, and naturally dried to obtain a glass tube with one end sealed for forming a copper film.

(5. Application of Metal Film-Forming Composition to Glass Tube (Substrate))
80 g of each of the five types of compositions for forming a metal film prepared in 3 above was poured into the washed and dried glass tubes with one end sealed, and the compositions were stored in the glass tubes. With the glass tubes standing upright, the openings of the glass tubes were sealed with rubber stoppers, and the glass tubes were placed vertically (upright) with the rubber stopper side facing upward at room temperature (23° C. to 25° C.), and left to stand for 3 days.
After being left to stand, the metal film-forming composition was discharged, washed five times with pure water, and then dried at room temperature. Three similar samples were prepared for each sample.
Visual observation confirmed that a copper film with metallic luster was formed on the inner surface of the glass tube.

(6. Evaluation of Metal Film)
The mass of the copper film formed in the glass tube and the resistance value of the formed metal film were measured.
The mass of the copper film was measured from the mass difference between the glass tube without the copper film and the glass tube after the copper film was formed. The measurement was performed for three samples, and the average value was taken as the mass of the copper film.

The resistance value of the obtained copper film was measured by the following method.
Five randomly selected points on the copper film near the opening of the glass tube were measured by the two-terminal measurement method, and the average value of the three points excluding the maximum and minimum values was taken as the resistance value. The same measurement device as in Example 5-1 was used.
The results are shown in Table 2 above.
From the results in Table 2, it was found that the resistance values of the copper films formed inside the glass tubes sealed at one end were all low, and that the copper films formed had electrical conductivity.
It is also apparent that the copper films formed in Examples 6-1 and 6-2, in which the copper ions were 200 parts and 300 parts per 100 parts of ascorbic acid, had lower resistance and better electrical conductivity.

[Examples 7-1 to 7-2]
(7. Consideration of the arrangement direction of the glass tube)
The metal film-forming composition (a) obtained in Example 6-1 (a composition containing 200 parts of copper ions per 100 parts of ascorbic acid) was used to study the copper film formation state depending on the arrangement direction of the glass tube.
80 g of the metal film-forming composition (a) obtained in Example 6-1 was poured into the one-end-sealed glass tube used in Example 6-1 and stored in the glass tube. With the glass tube standing upright, the opening of the glass tube was sealed with a rubber stopper. The glass tube was placed vertically (vertically placed) at room temperature (23° C. to 25° C.) with the rubber stopper side facing up and left to stand for 3 days. The copper film formed on the sample (Example 7-1) and the sample (Example 7-2) in which the glass tube was placed horizontally (horizontally placed) were evaluated.

In Example 7-2, the glass tube was first left standing horizontally for 24 hours, then the circumferential direction of the glass tube was inverted upside down (rotated 180°) and left standing horizontally for 24 hours, and then the circumferential direction was inverted upside down (rotated 180°) and left standing horizontally for 24 hours.
After 72 hours had passed, the state of the formed copper film was visually observed, and it was found that the copper film formed in Example 7-2 had better uniformity than that formed in Example 7-1.
The mass of the formed copper film and the resistance value of the copper film were measured in the same manner as in Example 6-1. In the horizontally placed sample of Example 7-2, the resistance values were measured for both the copper film on the side that was ultimately downward in the direction of gravity (the side that was downward for 48 hours) and the copper film on the upper side in the direction of gravity (the side that was downward for 24 hours).
The results are shown in Table 3.

According to Table 3, it can be seen that the mass of the copper film formed in Example 7-2 on the horizontally placed glass tube is greater than the mass of the copper film formed in Example 7-1, in which the film was formed on the vertically placed glass tube.
Furthermore, when the copper film was formed with the glass tube positioned sideways, the copper film formed on the inner surface of the glass tube located lower in the direction of gravity appeared thicker when observed visually than the copper film formed on the inner surface of the glass tube located higher in the direction of gravity.
The copper film formed on the lower part of the horizontally placed glass tube in the direction of gravity had a lower measured resistance and better electrical conductivity than the metal film formed on the inner surface of the glass tube on the upper side in the direction of gravity. Even when the glass tube was rotated, it was found that a thicker copper film was formed on the side that was in the lower position for a longer period of time.
From these findings, it can be inferred that when forming a copper film inside a glass tube, placing the tube horizontally relative to the direction of gravity is more useful for forming a uniform film than placing the tube vertically relative to the direction of gravity, and that rotating the glass tube up and down is also useful for reducing the effects of the direction of gravity.

[Examples 8-1 to 8-9]
(Preparation of Metal Film-Forming Composition)
In Example 5-1, the metal precursor liquid 2 obtained in (1.) and the ascorbic acid aqueous solution 2 obtained in (2.) were mixed in amounts of 100 parts, 200 parts, and 300 parts of copper ions per 100 parts of ascorbic acid, and stirred at room temperature and 500 rpm for 20 minutes to obtain a metal film-forming composition (i) having a copper ion content of 100 parts, a metal film-forming composition (ii) having a copper ion content of 200 parts, and a metal film-forming composition (iii) having a copper ion content of 300 parts. (Step II)

(Application of metal film-forming composition to substrate)
Four thoroughly cleaned quartz glass plates (length: 20 mm x width: 20 mm x thickness: 1.5 mm) were placed in a polystyrene plastic petri dish (diameter 90 mm, depth 15 mm).
30 g of each of the metal film-forming compositions (i) to (iii) obtained in step II was poured into a plastic petri dish, and a quartz glass plate was immersed in the metal film-forming compositions (i) to (iii) and allowed to stand at room temperature for one day.
The quartz glass plate after standing was removed from the plastic petri dish, washed five times with pure water, and then dried at room temperature to obtain copper film laminates of Examples 8-1, 8-4, and 8-7 in which a copper film was formed on the surface of the quartz glass plate. (Step III)
Copper film laminates of Examples 8-2, 8-5, and 8-8 were obtained in the same manner as above, except that the time for immersing in the metal film-forming compositions (i) to (iii) and leaving the metal film-forming compositions at rest was set to 2 days.
Copper film laminates of Examples 8-3, 8-6, and 8-9 were obtained in the same manner as above, except that the time for immersing in the metal film-forming compositions (i) to (iii) and leaving them at rest was set to 3 days.
The content ratio of copper ions relative to 100 parts of ascorbic acid and the immersion time in the metal film-forming composition are shown in Table 4 below.

(5. Evaluation of Metal Film)
The resistance value of the copper film thus formed was measured in the same manner as in Example 1. The mass of the copper film thus formed was measured in the same manner as in Example 7-1. The results are shown in Table 4.
As shown in Table 4, it was confirmed that an electrically conductive copper film was formed on each of the glass substrates.
Furthermore, in comparison with Examples 8-1, 8-4, and 8-7, it is found that the metal film-forming compositions containing 200 parts and 300 parts of copper ions per 100 parts of ascorbic acid formed copper films with a larger mass than the sample with a copper ion content of 100 parts. Furthermore, the copper films formed in the examples in which the metal film-forming composition was immersed for 3 days had better electrical conductivity than the samples in which the metal film-forming composition was immersed for 1 or 2 days.

[Examples 9-1 and 9-2]
(Preparation of Metal Film-Forming Composition)
A metal film-forming composition (a) (a composition containing 200 parts of copper ions per 100 parts of ascorbic acid) was obtained in the same manner as in Example 6-1.

(Application of metal film-forming composition to urethane substrate)
A block-type urethane foam (10 mm long x 10 mm wide x 60 mm long: light green color) and 35 g of the metal film-forming composition (a) obtained above were placed in a polyethylene bag (Japan Seisan Co., Ltd., Unipack E-4 (product name), length x width = 140 mm x 100 mm), the urethane foam was pressed about five times to push out the air inside the urethane foam with fingers, and the pressure was reduced for 30 minutes with a filter bell. Thereafter, the opening of the polyethylene bag was sealed, and the bag was left to stand at room temperature for 24 hours.
The urethane foam was then removed from the polyethylene bag, and the metal film-forming composition remaining in the voids was pushed out with fingers. The foam was then washed once using pure water as the washing water, after which the washing water was removed and the foam was dried at room temperature for 1 hour.
The obtained urethane foam turned brown, and it was confirmed that a copper film was formed on the surface. In this way, a urethane foam was obtained, which is the copper film laminate of Example 9-1 having a copper film. When the resistance value of the obtained copper film laminate of Example 9-1 was measured in the same manner as in Example 1, it was found to be 40 MΩ or more, and it was confirmed that the copper film laminate had electrical conductivity.

The copper film laminate of Example 9-1 was placed in the same polyethylene bag as above, and 35 g of the metal film-forming composition obtained above was placed in it. In the same manner, the air in the urethane foam was pushed out with fingers, and the pressure was reduced for 30 minutes with a filter. Then, the opening of the polyethylene bag was sealed, and the mixture was left at room temperature for 24 hours. Then, the urethane foam was taken out of the polyethylene bag, and the metal film-forming composition remaining in the voids was pushed out with fingers, and the mixture was washed once with pure water as washing water, after which the washing water was removed, and the mixture was dried at room temperature for 1 hour to obtain the copper film laminate of Example 9-2.
It was observed that the copper film laminate of Example 9-2 had a darker copper-derived brown color than the copper film laminate of Example 9-1.
When the resistance value of the obtained copper film laminate of Example 9-2 was measured in the same manner as in Example 8-1, it was found to be 40 MΩ or more, and it was confirmed that the copper film laminate had electrical conductivity.

(Industrial application field)
According to the metal film manufacturing method of the present disclosure, a metal film manufacturing method is provided that does not require heat treatment at 100° C. or higher and can easily form a dense metal film that has excellent adhesion to the substrate.
According to the manufacturing method disclosed herein, a metal film can be easily formed on any surface of a substrate of any shape, not just a flat plate, and a metal film that has good adhesion to the substrate can be formed even on a substrate that does not have heat resistance, making the method applicable to a variety of fields.
Furthermore, by applying the metal film-forming composition to the substrate and drying it multiple times, it is possible to easily form a metal film that is thicker and denser than a metal film obtained by applying the metal film-forming composition only once and drying it.
Metal films manufactured by the manufacturing method of the present disclosure are suitable for use in, for example, large-scale integrated circuit (LSI) circuits, solar cell wiring, trench-embedded wiring, electromagnetic wave shielding, infrared blocking glass, heat reflective glass, thermal conduction members for vacuum collectors, antibacterial materials such as antibacterial sponges that utilize the properties of silver or copper as a metal, heat transfer pipes, and the like.

10 Reactor 12 Filter 14 Flow path 16 Electrolyte tank (anode side electrolyte tank)
18 Electrolyte tank (cathode side electrolyte tank)
20 Electrolyte 22 Electrode (copper plate, anode)
24 Electrode (copper plate, cathode)
26 DC power supply 30 One-end sealed glass tube 32 Copper film 34 Measurement terminal 36 Conductor

Claims (14)

a step of reacting at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine in a mixed liquid containing at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent, to obtain a metal precursor liquid;
A step of preparing a composition for forming a metal film, the composition including the obtained metal precursor liquid and an organic reducing agent; and
applying the obtained metal film-forming composition to a substrate ;
the at least one metal selected from the group consisting of the metal complex and the metal salt includes at least one metal selected from the group consisting of silver, copper, lithium, nickel, manganese, zinc, and cobalt;
The method for producing a metal film , wherein the organic reducing agent contains at least one selected from the group consisting of ascorbic acid, citric acid, oxalic acid, and 3,4,5-trihydroxybenzoic acid . 2. The method for producing a metal film according to claim 1, wherein a metal film is obtained in which a content of a metal different from the metal contained in the at least one selected from the group consisting of metal complexes and metal salts is below a detection limit in an X-ray diffraction analysis in which X-ray diffraction intensity is measured for a 2θ of 10° to 80° in 0.05° steps at a fixed time of 5°/min using a parallel beam optical system with an incident angle of 0.3°. a step of reacting at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine in a mixed liquid containing at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent, to obtain a metal precursor liquid;
A step of preparing a composition for forming a metal film, the composition including the obtained metal precursor liquid and an organic reducing agent; and
applying the obtained metal film-forming composition to a substrate;
The process for obtaining the metal precursor liquid includes the steps of: storing an electrolytic solution containing at least one selected from ammonia and an amine in each of the pair of electrolytic solution tanks in a reaction apparatus having a pair of electrolytic solution tanks connected via a flow path equipped with a filter which does not allow metal ions to pass therethrough but allows hydrogen ions to pass therethrough; arranging metal electrodes in positions where at least a portion of the electrodes is in contact with the electrolytic solution; connecting the pair of electrodes via a DC power source; and applying a voltage between the pair of electrodes from the DC power source to react the electrolytic solution with metal ions in the electrolytic solution tank in which the electrode to be the anode is immersed. The method for manufacturing a metal film according to claim 3, wherein the metal ions are copper ions and the electrode is a copper electrode. The method for manufacturing a metal film according to claim 3 or 4, wherein the electrolytic solution contains ethylenediaminetetraacetic acid. The method for producing a metal film according to any one of claims 3 to 5, wherein the organic reducing agent includes at least one selected from compounds having a carboxy group. The method for producing a metal film according to any one of claims 3 to 6, wherein the organic reducing agent comprises at least one selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid. The method for producing a metal film according to any one of claims 1 to 7, wherein the step of applying the metal film-forming composition to the substrate includes at least one of the steps of applying the metal film-forming composition to the substrate, immersing the substrate in the metal film-forming composition, and storing the metal film-forming composition inside a container-shaped base. The method for producing a metal film according to any one of claims 1 to 8, further comprising a step of drying the metal film-forming composition applied to the substrate. a step of reacting at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine in a mixed liquid containing at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent, to obtain a metal precursor liquid;
A step of preparing a composition for forming a metal film, the composition including the obtained metal precursor liquid and an organic reducing agent; and
applying the obtained metal film-forming composition to a substrate;
The method further includes a step of drying the metal film-forming composition applied to the substrate,
A method for producing a metal film, comprising the steps of applying a metal film-forming composition to a substrate and drying the metal film-forming composition applied to the substrate multiple times. A metal precursor liquid containing a reaction product of at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine, and at least one organic reducing agent selected from the group consisting of ascorbic acid, citric acid, oxalic acid , and 3,4,5-trihydroxybenzoic acid;
the content of metal ions contained in the metal precursor liquid is in the range of 50 parts by mass to 400 parts by mass relative to 100 parts by mass of the organic reducing agent;
The at least one metal selected from the group consisting of the metal complexes and the metal salts comprises at least one metal selected from the group consisting of silver, copper, lithium, nickel, manganese, zinc, and cobalt . A non-conductive substrate; and
a metal precursor liquid including a reaction product of at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine, and at least one organic reducing agent selected from the group consisting of ascorbic acid, citric acid, oxalic acid , and 3,4,5-trihydroxybenzoic acid, on the non-conductive base material, wherein the content of metal ions contained in the metal precursor liquid is in the range of 50 parts by mass to 400 parts by mass per 100 parts by mass of the organic reducing agent;
A method for producing a metal film laminate having a metal film which is a cured product obtained by curing a composition for forming a metal film, wherein the at least one metal selected from the group consisting of the metal complexes and the metal salts contains at least one metal selected from the group consisting of silver, copper, lithium, nickel, manganese, zinc, and cobalt . 13. The method for producing a metal film laminate according to claim 12, wherein the content of the metal different from the metal contained in at least one selected from the group consisting of a metal complex and a metal salt is below the detection limit in an X-ray diffraction analysis in which X-ray diffraction intensity is measured for a 2θ of 10° to 80° in 0.05° steps at a fixed time of 5°/min using a parallel beam optical system with an incident angle of 0.3° against the metal film . The method for producing a metal film laminate according to claim 12 or 13, wherein the non-conductive base material contains a resin having at least one of a deflection temperature under load as defined in JIS K7191 (2015) and a continuous heat resistance temperature as determined by a long-term heat resistance continuous test (UL-746B (2013)) of less than 150°C.