WO2019138706A1

WO2019138706A1 - Method for producing conductive film, and conductive film

Info

Publication number: WO2019138706A1
Application number: PCT/JP2018/043490
Authority: WO
Inventors: 和史小村
Original assignee: 富士フイルム株式会社
Priority date: 2018-01-15
Filing date: 2018-11-27
Publication date: 2019-07-18
Also published as: JP6905089B2; TWI790326B; TW201932545A; JPWO2019138706A1

Abstract

Provided is a method for producing a conductive film, which comprises: an application step for forming a coating film by applying a composition for forming a conductive film to the surface of a substrate, said composition containing copper particles, at least one reducing agent that is selected from the group consisting of reductones and hydroxycarboxylic acids that have two or more carboxy groups and one or more hydroxy groups in each molecule, and a dispersion medium; a drying step for obtaining a dried film on the substrate by drying the coating film in an oxidizing atmosphere at a temperature of 150°C or less, said dried film being composed of a lower layer that does not substantially contain an oxide of copper and an upper layer that is arranged on the lower layer and contains an oxide of copper; and a separation step for obtaining a conductive film by removing the upper layer from the dried film. Also provided is a conductive film.

Description

Method of manufacturing conductive film and conductive film

The present invention relates to a method of manufacturing a conductive film and a conductive film.

Copper fine particles are widely used as raw materials for conductive coating agents, for example, because they are excellent in conductivity and inexpensive compared to metals such as silver. Such conductive coating agents are widely used as materials for forming circuits in printed wiring boards and the like using various printing methods, various electric contact members, and the like.

Further, in recent years, in order to meet the demand for miniaturization and high functionality of electronic devices, in the printed wiring board etc., further miniaturization and high integration of wiring are progressing. Along with this, it is required to be able to form a conductive film showing excellent conductivity on a substrate.

For example, Patent Document 1 describes a fibrous copper particulate composition comprising fibrous copper particulates, a dispersion medium, and a reducing compound having no amino group (claim 1). ).

JP 2014-118586 A

Further, from the viewpoint of reducing the manufacturing cost of the conductive film, etc., it is required to exhibit excellent conductivity even when the film is formed in an oxidizing atmosphere such as the air.

As a result of investigation by the present inventor, the conductive film formed in the air by applying the composition described in Patent Document 1 on a substrate does not reach the level of conductivity, and exhibits excellent conductivity. I could not get

Therefore, the present invention provides a method for producing a conductive film and a conductive film capable of forming a conductive film exhibiting excellent conductivity even when film formation is performed in an oxidizing atmosphere such as the air. To be an issue.

As a result of intensive studies to solve the above problems, the inventor selected from the group consisting of copper particles, reductone and hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule. A coating step of applying a composition for forming a conductive film containing at least one reducing agent to be added and a dispersion medium to the surface of a substrate to form a coating, and the coating under an oxidative atmosphere at 150.degree. The dried film is dried at the following temperature to obtain a dried film comprising an upper layer containing copper oxide and located on the opposite side of the substrate and a lower layer substantially free of copper oxide and located on the side of the substrate According to the method for manufacturing a conductive film, including the steps and the peeling step of removing the upper layer from the dried film to obtain the conductive film, the film is excellent even when the film is formed in an oxidizing atmosphere such as the air. It is possible to form a conductive film showing conductivity Become known the door, it has led to the completion of the present invention.
That is, the present invention provides the following [1] to [12].

[1] A copper particle, at least one reducing agent selected from the group consisting of reductone and hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule, and a dispersion medium Applying a composition for forming a conductive film on the surface of a substrate to form a coating film;
The coating film is dried at a temperature of 150 ° C. or less under an oxidative atmosphere to include a lower layer substantially free of copper oxides and an oxide of copper disposed on the lower layers on the substrate. Obtaining a dried film comprising an upper layer,
A peeling step of removing the upper layer from the dry film to obtain a conductive film.
[2] The method for producing a conductive film according to the above [1], wherein the (111) peak of Cu ₂ O by the X-ray diffraction method is detected in the upper layer and not detected in the lower layer.
[3] The method for producing a conductive film according to the above [1] or [2], wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, ascorbic acid derivatives and citric acid.
[4] The method for producing a conductive film according to any one of the above [1] to [3], wherein the average particle diameter of the copper particles is in the range of 25 to 1500 nm.
[5] The conductive film according to any one of the above [1] to [4], further comprising a heating step of heating the conductive film at a temperature of 150 ° C. or more and 190 ° C. or less after the peeling step. Production method.
[6] The method for producing a conductive film according to any one of the above [1] to [5], wherein the temperature in the drying step is 125 ° C. or less.
[7] The method for producing a conductive film according to any one of the above [1] to [6], wherein the composition for forming a conductive film does not contain a binder.
[8] The method for producing a conductive film according to any one of [1] to [7], wherein the ratio of the mass of the copper particles to the mass of the reducing agent is 90 to 99 mass%.
[9] A conductive film comprising copper and at least one reducing agent selected from the group consisting of reductone and a hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule. ,
The electrically conductive film whose content of the said copper is 90 mass% or more with respect to the total mass of the said electrically conductive film.
[10] The conductive film according to the above [9], wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, ascorbic acid derivatives and citric acid.
[11] The conductive film according to the above [9] or [10] which does not contain a binder.
[12] The conductive film according to any one of the above [9] to [11], wherein the (111) peak of Cu ₂ O is not detected by the X-ray diffraction method.

According to the present invention, there is provided a method of manufacturing a conductive film and a conductive film capable of forming a conductive film exhibiting excellent conductivity even when forming a film in an oxidizing atmosphere such as the air. be able to.

FIG. 1A is a schematic view showing a substrate before forming a coating film. FIG. 1B is a schematic view showing a state in which a coating film is formed on the surface of a substrate. FIG. 1C is a schematic view showing a state in which a dried film in which the lower layer (conductive film) and the upper layer are in contact at the interface is formed on the surface of the substrate. FIG. 1D is a schematic view showing a state in which the lower layer (conductive film) is formed on the surface of the substrate after removing the upper layer. FIG. 2 is a graph showing the XRD measurement results of Example 2 and Comparative Example 1. In Comparative Example 1 and cuprous oxide (informative), the baseline is indicated by being raised by the count shown in the parenthesis.

The conductive film and the method for producing the conductive film of the present invention will be described in detail below.
In the present specification, a range represented by using “to” means a range including both ends described before and after “to” in the range.

[Method of manufacturing conductive film]
The method for producing a conductive film of the present invention comprises at least one reducing agent selected from the group consisting of copper particles, reductone and hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule. And applying a composition for forming a conductive film containing a dispersion medium to the surface of a substrate to form a coated film, and drying the coated film at a temperature of 150 ° C. or less under an oxidative atmosphere, A drying step of obtaining a dry film comprising a lower layer substantially free of copper oxide and an upper layer comprising copper oxide disposed on the lower layer on the substrate, and removing the upper layer from the dry film And a peeling step of obtaining a conductive film.

The outline of the method for producing a conductive film of the present invention will be described with reference to FIGS. 1A to 1D.
A substrate 11 is prepared (FIG. 1A), and a composition for forming a conductive film is applied to the surface of the substrate 11 to form a coating film 12 (FIG. 1B).
Next, the coating film 12 formed on the surface of the substrate 11 is dried at a temperature of 150 ° C. or less in an oxidative atmosphere to form a dry film 13 (FIG. 1C). The dry film 13 has a structure divided at the interface 16 into the lower layer (conductive film) 14 on the surface side of the substrate 11 and the upper layer 15 on the opposite side to the substrate 11 (FIG. 1C). This is because the copper particles near the surface opposite to the substrate 11 side of the coating film 12 are oxidized by drying in an oxidizing atmosphere, and the copper particles are fused on the substrate 11 side of the coating film 12 Metal conductor is formed. During drying, a concentration imbalance of the reducing agent occurs in the thickness direction in the coating film 12, and since the oxygen concentration is high and the reducing agent concentration is low in the upper layer 15 of the dry film 13, copper oxidation progresses and the lower layer of the dry film 13 In 14, since the oxygen concentration is low and the reductant concentration is high, the oxidation of copper is suppressed. An interface 16 is formed between the upper layer 15 and the lower layer 14. By removing the upper layer 15, the lower layer (conductive film) 14 including the metal conductor can be obtained as a conductive film excellent in conductivity (FIG. 1D).
Each step will be described in detail below.

<Coating process>
In the coating step, the composition for forming a conductive film is applied to the surface of a substrate to form a coating film.

<< Composition for forming conductive film >>
The composition for forming a conductive film used in the method for producing a conductive film of the present invention is selected from the group consisting of copper particles, reductone and hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule. And at least one reducing agent, and a dispersing medium.

The mass ratio of the copper particles to the reducing agent in the composition for forming a conductive film is not particularly limited, but it is preferably 90 mass% to 99 mass%, as a ratio of mass of copper particles to mass of reducing agent. % To 97% by mass is more preferable, 91% by mass to 95% by mass is more preferable, and 93% by mass to 95% by mass is more preferable.
When the mass ratio of the copper particles to the reducing agent is within this range, the conductivity of the obtained conductive film is further improved.

The content of the dispersion medium in the composition for forming a conductive film is not particularly limited, but it is preferably 1 part by mass to 10000 parts by mass, and more preferably 10 parts by mass to 500 parts by mass with respect to 100 parts by mass of the copper particles. Preferably, 20 parts by mass to 200 parts by mass is more preferable.
When the content of the dispersion medium is in this range, the conductivity of the obtained conductive film becomes better.

(Copper particles)
The copper particles are to be metal conductors in the conductive film. By drying the composition for forming a conductive film applied to the substrate, the copper particles are fused to form a metal conductor in the conductive film.
As said copper particle, the conventionally well-known copper particle generally used to the composition for electrically conductive film formation can be used. The copper particles may be primary particles or secondary particles. Moreover, the shape of the said copper particle is not specifically limited, A spherical shape may be sufficient and plate shape may be sufficient.
The average particle size of the copper particles is not particularly limited, and in the case of primary particles, it is the average particle size of primary particles, and in the case of secondary particles, it is the average particle size of secondary particles, but 25 nm to 1500 nm. Is preferably 200 nm to 1500 nm, and more preferably in the range of 500 nm to 1500 nm.
In addition, the average particle diameter of copper particle (A) measures the Feret diameter of 100 particle | grains randomly selected from the scanning electron microscope (it may be hereafter mentioned "SEM") image, and this measurement. It is calculated by arithmetically averaging the values.

(Reductant)
The reducing agent is at least one selected from the group consisting of reductone and hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule.

((Reducton))
The reductone means an organic compound represented by the following formula (I) or the following formula (II) and having a structure in which a carbonyl group is bonded next to an enediol structure (hereinafter referred to as "reductone structure") . Reductone is an organic acid having reducibility and high acidity.

Representative examples of the above reductones are glycic acid represented by the following formula (Ia), reductic acid represented by the following formula (Ib), and ascorbic acid and ascorbic acid derivatives described later, but are limited thereto is not.

The reducing agent is preferably at least one member selected from the group consisting of ascorbic acid, ascorbic acid derivatives and citric acid, more preferably at least one member selected from the group consisting of ascorbic acid and ascorbic acid derivatives, and ascorbic acid More preferable.

(((Ascorbic acid)))
The ascorbic acid is a compound represented by (2R) -2-[(1S) -1,2-dihydroxyethyl] -3,4-dihydroxy-2H-furan-5-one (formula (A-1) below) The present compound may be referred to as "in a narrow sense ascorbic acid" or "L-ascorbic acid"), (2S) -2-[(1R) -1,2-dihydroxyethyl] -3,4-dihydroxy- 2H-furan-5-one (compound represented by the following formula (A-2); the present compound may be referred to as “D-ascorbic acid”), (2S) -2-[(1S) -1 2, 2-Dihydroxyethyl] -3,4-dihydroxy-2H-furan-5-one (compound represented by the following formula (A-3); this compound may be referred to as "L-isoascorbic acid". And (2R) -2-[(1R) -1,2-dihydroxyethyl] -2,3-dihydroxy-2H-furan-5-one (compound represented by the following formula (A-4)); “Erythorbic acid” or “D-isoascorbi” It is at least one compound selected from the group consisting of may be referred to as acid ".).

(((Ascorbic acid derivative)))
The ascorbic acid derivative is a compound represented by the following general formula (B-1) (sometimes referred to as "ascorbic acid derivative (B-1)") or a compound represented by the following general formula (B-2) (It may be referred to as "ascorbic acid derivative (B-1)") is preferred.
The reducing power for copper oxides is due to the enediol structure in the ascorbic acid derivative. Therefore, it is also possible to synthesize a derivative of ascorbic acid in a form that leaves its structure, and use it by appropriately adjusting the solubility and polarity.

・ Ascorbic acid derivative represented by general formula (B-1)

In Formula (B-1), R ¹ and R ² each independently represent a hydrogen atom or an acyl group which may have a substituent. However, R ¹ and R ² do not simultaneously represent a hydrogen atom.

The acyl group for R ¹ and R ² in the above general formula (B-1) is not particularly limited, and a linear, branched, monocyclic or condensed polycyclic aliphatic group having 1 to 18 carbon atoms is bonded Preferred is a carbonyl group or a carbonyl group to which a monocyclic or fused polycyclic aryl group having 6 to 10 carbon atoms is bonded.

Specific examples of the above acyl group are formyl group, acetyl group, propionyl group, butyryl group, isobutyryl group, valeryl group, isovaleryl group, pivaloyl group, lauroyl group, myristoyl group, palmitoyl group, stearoyl group, cyclopentyl carbonyl group, cyclohexylcarbonyl And any one selected from the group consisting of acryloyl group, methacryloyl group, crotonoyl group, isocrotonoyl group, oleoyl group, benzoyl group, 1-naphthoyl group and 2-naphthoyl group, but is limited thereto It is not a thing.

In each of the acyl groups, a hydrogen atom in the acyl group may be substituted by a substituent, and it is also possible to further adjust the solubility and the polarity.
Although the specific example of the said substituent is one or more types of substituents selected from the group which consists of a hydroxyl group and a halogen atom, it is not limited to these.

A representative example of the ascorbic acid derivative (B-1) is one represented by the following formula (B-1-X). However, the ascorbic acid derivative (B-1) in the present invention is not limited to these representative examples.

However, in the above formula (B-1-X), X represents any one selected from the group consisting of chemical structures shown below. In each chemical structure, "*" indicates a position at which X binds to the five-membered ring site of ascorbic acid.

・ General formula (B-2)

In Formula (B-2), R ³ and R ⁴ each independently represent a hydrogen atom or an alkyl group which may have a substituent.

The compound represented by the general formula (B-2) is an ascorbic acid derivative in which an acetal structure or a ketal structure is formed by reacting two hydroxyl groups present in the side chain of ascorbic acid with an aldehyde or ketone.

The alkyl group for R ³ and R ⁴ in the general formula (B-2) is not particularly limited, but is preferably a linear, branched, monocyclic or fused polycyclic alkyl group having 1 to 18 carbon atoms.

Specific examples of the above alkyl group are methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, octadecyl group, isopropyl group, isobutyl group, Isopentyl group, sec-butyl group, tert-butyl group, sec-pentyl group, tert-pentyl group, tert-octyl group, neopentyl group, cyclopropyl group, cyclobutyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, adamantyl group, norbornyl group and Although it is any one selected from the group consisting of 4-decylcyclohexyl group, it is not limited thereto.

In each of the above alkyl groups, a hydrogen atom in the alkyl group may be substituted by a substituent, whereby the solubility and the polarity can be further adjusted.
Although the specific example of the said substituent is one or more types of substituents selected from the group which consists of a hydroxyl group and a halogen atom, it is not limited to these.

The R ³ and the R ⁴ may be integrated to form a ring structure.

A representative example of the ascorbic acid derivative (B-2) is one represented by the following formula (B-2-Y). However, the ascorbic acid derivative (B-2) in the present invention is not limited to these representative examples.

However, in the above formula (B-2-Y), Y represents any one selected from the group consisting of chemical structures shown below. Note that "*" in each chemical structure indicates the position at which Y binds to the five-membered ring site of ascorbic acid.

((Hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule))
The hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule is not particularly limited, but a hydroxycarboxylic acid having three or more carboxy groups and one or more hydroxy group in the molecule Is preferred.
Examples of hydroxycarboxylic acids having two or more carboxy groups and one or more hydroxy groups in the above molecule are, but not limited to, citric acid and isocitric acid.
In the conductive film of the present invention, the hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule is at least one hydroxycarboxylic acid selected from the group consisting of citric acid and isocitric acid. Is preferred, and citric acid is more preferred.

(Dispersion medium)
The dispersion medium is not particularly limited as long as it can dissolve or disperse the reducing agent.
Specific examples of the dispersion medium include water, methanol, ethanol, propanol, 2-propanol, cyclohexanone, cyclohexanol, terpineol, ethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol At least one member selected from the group consisting of monobutyl ether acetate, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate, consisting of water, methanol, ethanol, propanol and 2-propanol Little selected from the group Both are preferred one, water, more preferably at least one selected from the group consisting of methanol and ethanol, water is further preferred. As the water, ion exchange water, RO (Reverse Osmosis) water, distilled water or other pure water, or ASTM D 1193-06 type 1 grade other ultra pure water is preferable.

(Preparation method of composition for conductive film formation)
Although the preparation method of the composition for electrically conductive film formation used in the manufacturing method of the electrically conductive film of this invention is not specifically limited, For example, it can be made to describe below.

((Mixture of copper particles, reducing agent and dispersion medium))
The method of mixing the copper particles, the reducing agent, and the dispersion medium is not particularly limited, and a conventionally known method can be adopted.
For example, after copper particles and a reducing agent are added to the dispersion medium, ultrasonic wave (for example, treatment with an ultrasonic homogenizer), mixer method, three-roll method, and ball mill method can be used. The composition can be obtained by dispersing the components.

((Reduction of copper oxide))
After mixing the copper particles, the reducing agent, and the dispersion medium, it is preferable to carry out reduction treatment of the copper oxide.
Specifically, for example, it is preferable to put a mixture of copper particles, a reducing agent, and a dispersion medium in a closed container, shut off air, and leave still for 48 hours or more in the absence of oxygen. The temperature upon standing is preferably 1 ° C. to 30 ° C.
By reducing the copper oxide, the conductivity of the obtained conductive film becomes better.

(binder)
The composition for forming a conductive film preferably does not contain a binder. The binder usually has an effect of improving the adhesion of the conductive film to the substrate, but in the conductive film of the present invention, it is not preferable to contain the binder because the conductivity may be reduced.
Here, as the binder, a resin and an organic compound having a molecular weight of 200 or more can be mentioned.

As said resin, a thermosetting resin and a thermoplastic resin are mentioned.
Specific examples of the thermosetting resin are phenol resin, epoxy resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, oligoester acrylate resin, xylene resin, bismaleide triazine resin, furan resin, urea resin, polyurethane, Examples thereof include melamine resin, silicone resin, acrylic resin, oxetane resin and oxazine resin, and specific examples of the thermoplastic resin include polyamide resin, polyimide resin, acrylic resin, ketone resin, polystyrene resin and thermoplastic polyester resin. It is not limited to these.

The organic compound having a molecular weight of 200 or more is not particularly limited, and examples thereof include an organic acid having a molecular weight of 200 or more, a polyalkylene glycol having a molecular weight of 200 or more, a sugar alcohol having a molecular weight of 200 or more, an oligosaccharide and a polysaccharide.

"substrate"
A conventionally known substrate can be used as the substrate.
In addition, specific examples of the material used for the substrate are resin, paper, glass, silicon semiconductor, compound semiconductor, metal, metal oxide, metal nitride, wood, or a composite thereof. It is not limited.

Specific examples of the resin are low density polyethylene resin, high density polyethylene resin, ABS (Acrylonitrile Butadiene Styrene) resin, acrylic resin, styrene resin, vinyl chloride resin, polyester resin (polyethylene terephthalate (PET)), polyacetal resin, polysulfone resin And polyether imide resins, polyether ketone resins, polyimide resins, and cellulose derivatives, but are not limited thereto.
Specific examples of the above-mentioned paper are coated printing paper, fine coated printing paper, coated printing paper (art paper, coated paper), special printing paper, copy paper (PPC paper), non-bleached wrapping paper (both for heavy bags) Other examples include, but are not limited to, kraft paper, double kraft paper), bleached wrapping paper (bleached kraft paper, pure white roll paper), coated balls, chip balls, and corrugated boards.
Specific examples of the above-mentioned glass are soda glass, borosilicate glass, silica glass and quartz glass, but are not limited thereto.
Specific examples of the silicon-based semiconductor are amorphous silicon and polysilicon, but are not limited thereto.
Specific examples of the compound semiconductor are CdS, CdTe and GaAs, but are not limited thereto.
Specific examples of the above-mentioned metals are copper, iron and aluminum, but not limited thereto.
Specific examples of the above metal oxides are alumina, sapphire, zirconia, titania, yttrium oxide, indium oxide, ITO (indium tin oxide), IZO (indium zinc oxide), nesa (tin oxide), ATO (antimony doped oxide) Tin), fluorine-doped tin oxide, zinc oxide, AZO (aluminum-doped zinc oxide), and gallium-doped zinc oxide, but are not limited thereto.
Although the specific example of the said metal nitride is aluminum nitride, it is not limited to this.
Further, specific examples of the above-mentioned composites are paper-phenol resin, paper-epoxy resin, paper-resin composite such as paper-polyester resin, glass cloth-epoxy resin (glass epoxy resin), glass cloth-polyimide resin, And glass cloth-fluoroplastics, but is not limited thereto.
The substrate on which the conductive film of the present invention is formed is not particularly limited, but a glass substrate, a polyimide substrate, or a polyethylene terephthalate (PET) substrate is preferable.

<< Method for applying a composition for forming a conductive film on a substrate >>
The method for applying the composition for forming a conductive film on a substrate is not particularly limited, and a known method can be adopted. For example, coating methods such as screen printing method, dip coating method, spray coating method, spin coating method, and inkjet method can be mentioned.
The shape of the coating is not particularly limited, and may be a surface covering the entire surface of the substrate or a pattern (for example, a wiring or a dot).

The coating amount of the composition for forming a conductive film on a substrate may be appropriately adjusted according to the desired film thickness of the conductive film, but generally, the film thickness (thickness) of the coating film is preferably 2 μm to 600 μm. 10 μm to 300 μm is more preferable, and 10 μm to 200 μm is more preferable.

<Drying process>
In the drying step, the coating is dried in an oxidative atmosphere at a temperature of 150 ° C. or less to form a lower layer substantially free of copper oxides and a lower layer of copper on the substrate. A dry film comprising an upper layer containing an oxide is obtained. The dry film has a lower layer and an upper layer in this order from the substrate side.

In the drying step, the formed coating is dried in an oxidative atmosphere to remove the dispersion medium. The upper layer is formed by removing the dispersion medium remaining in the coating film and forming a metal conductor by fusion of copper particles on the side close to the substrate of the coating film and forming copper oxide on the surface side of the coating film. A dry film separated from the interface is obtained as the lower layer and the lower layer.

Examples of oxidative atmospheres include, but are not limited to, atmospheres containing oxygen, such as in air or air.

As a method of drying, a method of drying using a hot air dryer or the like can be used.

The temperature during drying (hereinafter sometimes referred to as “drying temperature”) is not particularly limited as long as it is 150 ° C. or less, but 0 ° C. to 150 ° C. is preferable, 0 ° C. to 125 ° C. is more preferable, and 4 ° C. 100 ° C. is more preferred.
When the temperature during drying is higher than 150 ° C., the oxidation of copper exceeds the rate of oxidation of copper oxide by the reducing agent, and a conductive film exhibiting desired conductivity can not be obtained.

The time for drying (hereinafter sometimes referred to as "drying time") is not particularly limited, but is preferably 1 second to 96 hours, more preferably 5 seconds to 72 hours, and still more preferably 10 seconds to 48 hours. However, the drying time may be set as appropriate depending on the drying temperature as long as substantially all of the dispersion medium can be removed from the coating film.

<Peeling process>
In the peeling step, the upper layer is removed from the dried film to obtain a conductive film.
Although the method of removing the upper layer is not particularly limited, a method of scraping the upper layer with a device such as a scraper or a method of wiping the upper layer with a waste such as Kimwipe may be mentioned.
In the present step, the entire upper layer is removed.
The conductive film obtained by the method for producing a conductive film of the present invention is substantially free of an oxide of copper because the reduction agent coexisting with copper suppresses the oxidation of copper.
Here, it is measured by X-ray diffraction (XRD: X-ray diffraction) method that substantially no copper oxide is contained, and the (111) peak derived from copper oxide (I) [Cu ₂ O] is It means that it is not detected, and that the oxide of copper is contained means that a (111) peak derived from copper oxide (I) [Cu ₂ O] is detected by X-ray diffraction method.

In addition, the measurement conditions of X-ray diffraction shall be described below here.
X-ray diffractometer RINT Ultima III X-Ray Diffractometer (manufactured by RIGAKU Co., Ltd.)
2Θ / ω 30-45 degree sampling step 0.01 degree scan speed 10 degree / minute attenuator (ATT: Attenuator) Opening divergence slit (DS: Dvergence slit) 1.00 mm
Scattering slit (SS: Scattering slit) Open Light receiving slit (RS: Receiving slit) Open Optical system parallel slit PB
Incident vertical limited solar slit V5
Vertical restriction slit 10 × 10
Parallel slit analyzer PSA

Note that “the (111) peak of copper oxide (I) [Cu ₂ O] is not detected” by the X-ray diffraction method means the (111) peak intensity of Cu ₂ O measured under the conditions of the above X-ray diffraction and The ratio Z of the (111) peak intensity of Cu (Z ≡ {(111) peak intensity of Cu ₂ O / (111) peak intensity of Cu} × 100 (%)) means less than 0.1% Here, “detecting” the (111) peak of copper oxide (I) [Cu ₂ O] by X-ray diffraction means that the above-mentioned Z is 0.1% or more.

<Heating process>
The method for producing a conductive film of the present invention may further include a heating step of heating the obtained conductive film at a temperature of more than 150 ° C. and 190 ° C. or less after the peeling step, as desired.
By performing the heating step, the conductivity of the conductive film becomes better.

The means for heating is not particularly limited, and known heating means such as an oven and a hot plate can be used.

The temperature at the time of heating is preferably 155 ° C. to 190 ° C., more preferably 160 ° C. to 190 ° C., and still more preferably 160 ° C. to 180 ° C. in that a conductive film having better conductivity can be formed.

The time for heating is not particularly limited, and is preferably 1 minute to 120 minutes, more preferably 5 minutes to 60 minutes, and 5 minutes to 30 minutes in that a conductive film having excellent conductivity can be formed. More preferable.

The atmosphere at the time of heating is not particularly limited, and may be performed in any of non-oxidative atmosphere and oxidative atmosphere.
As said non-oxidative atmosphere, inert gas atmospheres, such as nitrogen and argon, and reducing gas atmospheres, such as hydrogen, etc. are mentioned. Moreover, as said oxidative atmosphere, an air | atmosphere atmosphere, and oxygen atmosphere etc. are mentioned.

[Conductive film]
The conductive film of the present invention contains copper and at least one reducing agent selected from the group consisting of reductone and hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule, The content of copper is 90% by mass or more with respect to the total mass of the conductive film.

<Copper / Reductant>
The copper is metal copper.
The content of copper in the conductive film is not particularly limited as long as it is 90% by mass or more of the total mass of the conductive film, but 93% by mass or more and less than 100% by mass is preferable, and 95% by mass or more and less than 100% by mass More preferably, 97% by mass or more and less than 100% by mass are more preferable.
Here, the copper content in the conductive film is obtained by dissolving the scraped conductive film in nitric acid and analyzing the copper concentration in the solution by X-ray fluorescence (XRF) analysis. It can be measured by

The XRF measurement was performed using a fluorescent X-ray analyzer (Axios, manufactured by PANalytical) under the following measurement conditions.
Line: K α ray Crystal: LIF 200
Collimator: 150 um
Detector: Duplex
Tube filter: None Voltage: 60kV
Current: 60 mA
Measurement time: 40 seconds Irradiated area: 20φ

The copper contained in the conductive film of the present invention is preferably in the state in which a plurality of copper particles are fused to form a conductor.
In addition, the said copper particle is the same as that of what was described in the manufacturing method of the electrically conductive film of this invention.

The reducing agent contained in the conductive film of the present invention is the same as that described in the method of producing a conductive film of the present invention.

In the conductive film of the present invention, since copper and a reducing agent coexist in the conductive film, the formation of copper oxide by the reaction between metallic copper and oxygen in the air is suppressed, and excellent conductivity over a long period of time Can be maintained.
In the conductive film of the present invention, since a reducing agent is present, if copper (I) oxide is not present in the conductive film, no copper oxide other than copper (I) oxide such as copper (II) oxide is also present. It can be regarded as
Therefore, that the conductive film of the present invention does not contain a copper oxide is measured by X-ray diffraction (XRD: X-ray diffraction) method, in which the conductive film and the air are in contact and the surface of the conductive film is most easily oxidized. It can be judged that the peak derived from copper oxide (I) is not detected.
Accordingly, the conductive film of the present invention is preferably one in which the (111) peak of copper oxide (I) [Cu ₂ O] is not detected by the X-ray diffraction method.

Here, the measurement conditions of X-ray diffraction shall be described below.
X-ray diffractometer RINT Ultima III X-Ray Diffractometer (manufactured by RIGAKU Co., Ltd.)
2Θ / ω 30-45 degree sampling step 0.01 degree scan speed 10 degree / minute attenuator (ATT: Attenuator) Opening divergence slit (DS: Dvergence slit) 1.00 mm
Scattering slit (SS: Scattering slit) Open Light receiving slit (RS: Receiving slit) Open Optical system parallel slit PB
Incident vertical limited solar slit V5
Vertical restriction slit 10 × 10
Parallel slit analyzer PSA

<binder>
The conductive film of the present invention preferably contains no binder.
In addition, the said binder is the same as that described in the manufacturing method of the electrically conductive film of this invention.

<Thickness of conductive film>
The thickness of the conductive film of the present invention is not particularly limited, but is preferably 1 μm to 100 μm, more preferably 1 μm to 50 μm, and still more preferably 1 μm to 30 μm.
When the thickness of the conductive film of the present invention is within the above range, a conductive film having sufficient film strength is obtained in the step of peeling the lower layer substantially free of copper oxide and the upper layer containing copper oxide be able to.

<substrate>
The conductive film of the present invention is preferably formed on a substrate.
The substrate is the same as that described in the method for producing a conductive film of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1
<Preparation of composition for conductive film formation>
10 parts by mass of copper particles (average particle size 750 nm; manufactured by Mitsui Metals Co., Ltd.) and 1.8 parts by mass of L-ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed with 18.2 parts by mass of ion exchanged water The mixture was well stirred at 2000 rpm for 5 minutes to obtain a mixture.
After stirring, the mixed solution is transferred to a closed container and kept in a sealed container at 25 ° C. for 48 hours to form a composition for forming a conductive film (hereinafter sometimes referred to as “the composition for forming a conductive film”) Obtained.

<Production of conductive film>
<< Application >>
A glass substrate (length 76 mm × width 26 mm × thickness 0.9 mm; manufactured by Matsunami Glass Co., Ltd.) was prepared.
On this glass substrate, the composition 1 for conductive film formation was apply | coated by coil bar to length 61 mm * width 26 mm * wet thickness 40 micrometers, and the coating film was formed in the surface of a glass substrate.

<< Drying >>
The coating film formed on the glass substrate was dried under the drying conditions shown in Table 1 to form a dried film on the glass substrate.

<< Peeling off >>
The surface of the dried film was rubbed with a Kimwipe to peel off the upper layer of the dried film to obtain a conductive film.

"heating"
The glass substrate on which the conductive film was formed was heated at 150 ° C. in the atmosphere for 1 hour.

<Measurement>
(1) Film Thickness Measurement The film thickness before peeling was determined by measuring the thickness of the dried film obtained in the drying step.
Further, the film thickness after peeling was determined by measuring the thickness of the conductive film obtained in the peeling step.
The film thickness was measured by scraping a part of the coating film with a metal spatula and using the surface shape measuring device (Dektak 150 Surface Profiler, manufactured by Veeco) to measure the difference between the substrate surface and the coating film surface.
The film thickness before peeling and the film thickness after peeling are shown in the column of “before peeling” and “after peeling” of “thickness [μm]” in Table 1, respectively.

(2) XRD measurement The XRD measurement before peeling was performed on the surface of the dried film obtained in the drying step.
In addition, XRD measurement after peeling was performed on the surface of the conductive film obtained in the peeling step.
The XRD measurement was performed using an X-ray diffractometer (RINT Ultima III X-Ray Diffractometer, manufactured by Rigaku Corporation) under the following measurement conditions.
2Θ / ω 30-45 degree sampling step 0.01 degree scan speed 10 degree / minute attenuator (ATT: Attenuator) Opening divergence slit (DS: Dvergence slit) 1.00 mm
Scattering slit (SS: Scattering slit) Open Light receiving slit (RS: Receiving slit) Open Optical system parallel slit PB
Incident vertical limited solar slit V5
Vertical restriction slit 10 × 10
Parallel slit analyzer PSA

The XRD measurement results were evaluated as follows.
A: A (111) peak derived from Cu ₂ O was not detected B: a (111) peak derived from Cu ₂ O was detected However, a (111) peak derived from Cu ₂ O was detected by "not detected", derived from the Cu ₂ O by XRD measurement (111) derived from the peak intensity and Cu (111) derived from the ratio Z [Z≡ {Cu ₂ O peak intensity (111) peak It means that (111) peak intensity derived from intensity / Cu} × 100 (%) is less than 0.1%, and “detected” means that Z is 0.1% or more. Say.
The XRD measurement results before peeling and the XRD measurement results after peeling are shown in the “before peeling” and “after peeling” columns of “XRD” in Table 1, respectively.

(3) Conductivity The measurement of the volume resistance value after peeling was performed about the conductive film obtained at the peeling process.
Moreover, the measurement of the volume resistance value after heating was performed about the electrically conductive film obtained at the heating process.
The volume resistance of the film was measured by the four probe method.
The measurement result of the volume resistance after peeling and the measurement result of the volume resistance after heating are shown in the “after peeling” and “after heating” columns of “volume resistance [Ω · m]” in Table 1, respectively. The

[Examples 2 to 4]
Example 2
A conductive film was formed in the same manner as in Example 1 except that the drying conditions of the coating film formed on the glass substrate were performed under the conditions shown in the "drying conditions" column of Table 1.
The thickness before peeling of the dried film and the thickness of the conductive film obtained by peeling the upper layer of the dried film are shown in the "before peeling" column and the "after peeling" column of the "thickness" column in Table 1, respectively.
The XRD measurement result before peeling of the dried film and the XRD measurement result of the conductive film obtained by peeling the upper layer of the dried film are shown in the “before peeling” column and the “after peeling” column of “XRD” column of Table 1.
The volume resistance value of the conductive film obtained by peeling the upper layer of the dried film and the volume resistance value after heating the conductive film are shown in the “after peeling” column and “heating” in the “volume resistance value” column of Table 1, respectively. It shows in the "after" column.
Moreover, the graph showing the XRD measurement result of the electrically conductive film of Example 2 is shown in FIG.

(4) Analysis of metallic copper and reducing agent in conductive film XRF measurement of metallic copper in the conductive film was performed using a fluorescent X-ray analyzer (Axios, manufactured by PANalytical) under the following measurement conditions.
Line: K α ray Crystal: LIF 200
Collimator: 150 um
Detector: Duplex
Tube filter: None Voltage: 60kV
Current: 60 mA
Measurement time: 40 seconds Irradiated area: 20φ

In addition, the content of ascorbic acid in the conductive film can be measured by adding a scraped conductive film to ion-exchanged water and performing ultrasonic irradiation for 10 minutes using a high-performance liquid chromatograph (Prominence-comprehensive HPLC series, The following measurement conditions were used using Shimadzu Corporation make).
Column: Shiseido CAPCELL PAK C18 AQ 5um
Guard column: None Flow rate: 0.8 ml / min
Column temperature: 40 ° C
Detection wavelength: 254 nm
Eluent: A: 25 mM potassium dihydrogen phosphate-phosphoric acid aqueous solution (pH = 2.5)
B: Methanol (without buffer)
Rinsing solution: water: methanol = 1: 1 (vol%)
Time program: 0 to 8.0 min: B.conc = 0%
8.01 to 13.0 min: B.conc = 80%
13.1 to 35.0 min: B. conc = 0%

As a result of the measurement as described above, the content of metallic copper in the conductive film was 92.2% by mass, and the content of ascorbic acid as a reducing agent was 7.8% by mass.

Example 3
A conductive film was formed in the same manner as in Example 1 except that the drying conditions of the coating film formed on the glass substrate were performed under the conditions shown in the "drying conditions" column of Table 1.
The thickness before peeling of the dried film and the thickness of the conductive film obtained by peeling the upper layer of the dried film are shown in the "before peeling" column and the "after peeling" column of the "thickness" column in Table 1, respectively.
The XRD measurement result before peeling of the dried film and the XRD measurement result of the conductive film obtained by peeling the upper layer of the dried film are shown in the “before peeling” column and the “after peeling” column of “XRD” column of Table 1.
The volume resistance value of the conductive film obtained by peeling the upper layer of the dried film is shown in the "after peeling" column of the "volume resistance value" column of Table 1.

Example 4
A conductive film was formed in the same manner as in Example 2 except that citric acid was used instead of L-ascorbic acid.
The thickness before peeling of the dried film and the thickness of the conductive film obtained by peeling the upper layer of the dried film are shown in the "before peeling" column and the "after peeling" column of the "thickness" column in Table 1, respectively.
The XRD measurement result before peeling of the dried film and the XRD measurement result of the conductive film obtained by peeling the upper layer of the dried film are shown in the “before peeling” column and the “after peeling” column of “XRD” column of Table 1.
The volume resistance value of the conductive film obtained by peeling the upper layer of the dried film is shown in the "after peeling" column of the "volume resistance value" column of Table 1.

[Comparative Examples 1 to 7]
Comparative Example 1
A dried film was formed on a glass substrate in the same manner as in Example 2 except that the composition for forming a conductive film was prepared according to the composition shown in Table 2.
When the surface of the dried film formed on the glass substrate was lightly wiped with Kimwipe, all the dried film was wiped off in the form of powder and peeled off completely.
The thickness before peeling of the dried film is shown in the "before peeling" column of the "thickness" column of Table 1, and the XRD measurement result before peeling is shown in the "before peeling" column of the "XRD" column of Table 1.
The volume resistance value after peeling off the dried film could not be measured.
Moreover, the graph showing the XRD measurement result of the dried film before peeling of Comparative Example 1 is shown in FIG.

Comparative Example 2
A dry film was formed on a glass substrate in the same manner as in Example 2, but the upper layer was not peeled off.
The thickness of the dried film is shown in the "before peeling" column of the "thickness" column of Table 1, the XRD measurement result is in the "before peeling" column of the "XRD" column of Table 1, and the measurement result of the volume resistance is shown in "Table 1". It shows in the "before peeling" column of "volume resistance value" column, respectively.

Comparative Example 3
A dry film was formed on a glass substrate in the same manner as in Example 2, but the upper layer was partially peeled off in the thickness direction.
The thicknesses before and after peeling of the dried film are shown in the "before peeling" column and the "after peeling" column of the "thickness" column of Table 1, respectively.
The XRD measurement result before peeling of a dried film is shown in the "before peeling" column of the "XRD" column of Table 1.
The volume resistance values before and after peeling of the dried film are shown in the "before peeling" column and the "after peeling" column in the "volume resistance value" column of Table 1, respectively.

Comparative Example 4
A composition for conductive film formation was prepared in the same manner as in Example 4 except that the reducing agent was changed to formic acid, to form a dry film and a conductive film on a glass substrate.
The thickness before peeling of the dried film and the thickness of the conductive film obtained by peeling the upper layer of the dried film are shown in the "before peeling" column and the "after peeling" column of the "thickness" column in Table 1, respectively.
The XRD measurement result before peeling of the dried film and the XRD measurement result of the conductive film obtained by peeling the upper layer of the dried film are shown in the “before peeling” column and the “after peeling” column of “XRD” column of Table 1.
The volume resistance value of the conductive film obtained by peeling the upper layer of the dried film is shown in the "after peeling" column of the "volume resistance value" column of Table 1.

Comparative Example 5
A composition for conductive film formation was prepared in the same manner as in Comparative Example 1 except that the reducing agent was changed to oxalic acid, and a dry film was formed on a glass substrate.
When the surface of the dried film formed on the glass substrate was lightly wiped with Kimwipe, all the dried film was wiped off in the form of powder and peeled off completely.
The thickness before peeling of the dried film is shown in the "before peeling" column of the "thickness" column of Table 1, and the XRD measurement result before peeling is shown in the "before peeling" column of the "XRD" column of Table 1.
The volume resistance value after peeling off the dried film could not be measured.

Comparative Example 6
A composition for conductive film formation was prepared in the same manner as in Comparative Example 1 except that the reducing agent was changed to acetic acid, and a dried film was formed on a glass substrate.
When the surface of the dried film formed on the glass substrate was lightly wiped with Kimwipe, all the dried film was wiped off in the form of powder and peeled off completely.
The thickness before peeling of the dried film is shown in the "before peeling" column of the "thickness" column of Table 1, and the XRD measurement result before peeling is shown in the "before peeling" column of the "XRD" column of Table 1.
The volume resistance value after peeling off the dried film could not be measured.

Comparative Example 7
A composition for conductive film formation was prepared in the same manner as in Example 4 except that the reducing agent was changed to L-cysteine, and a dry film and a conductive film were formed on a glass substrate.
The thickness before peeling of the dried film and the thickness of the conductive film obtained by peeling the upper layer of the dried film are shown in the "before peeling" column and the "after peeling" column of the "thickness" column in Table 1, respectively.
The XRD measurement result before peeling of the dried film and the XRD measurement result of the conductive film obtained by peeling the upper layer of the dried film are shown in the “before peeling” column and the “after peeling” column of “XRD” column of Table 1.
The volume resistance value of the conductive film obtained by peeling the upper layer of the dried film is shown in the "after peeling" column of the "volume resistance value" column of Table 1.

In Table 2, "total peeling" in the column of "thickness" indicates that the dried film is not completely separated as the upper layer and the lower layer, but the dried film is completely wiped off as powdery material, and all is peeled off, "volume resistance value" “NA” in the column of indicates that the volume resistance value could not be measured as a result of peeling of all the dried films.
In Table 2, "O.L." in the column of "volume resistance value" indicates that the volume resistance value is high and exceeds the measurement limit.
Further, “after peeling” in Comparative Example 3 represents a volume resistance value measured after partially removing the upper layer of the dried film in the thickness direction.

In Examples 1 to 4, after peeling off the dried film, a conductive film having excellent conductivity was obtained.
On the other hand, in Comparative Examples 1 to 7, the conductive film excellent in conductivity could not be obtained.

Comparative Example 1 is an example in which the composition for forming a conductive film does not contain a reducing agent.
In Comparative Example 1, the copper oxide is not reduced to metallic copper, and the upper layer containing copper oxide and the lower layer containing metallic copper are not formed even if the coated film is dried, and the dried film is dried when wiped with a kimwipe The entire membrane has been wiped off as a powder. Therefore, a conductive film excellent in conductivity could not be obtained.

Comparative Examples 2 and 3 were the same as Example 2 until the dried film was formed on the substrate, but the upper layer of the dried film was not peeled off (Comparative Example 2), or the upper layer of the dried film was in the thickness direction The film was only partially peeled off (Comparative Example 3).
In Comparative Examples 2 and 3, since the upper layer was not completely removed, a conductive film having excellent conductivity could not be obtained.

Comparative Examples 4 to 7 are examples using formic acid (Comparative Example 4), oxalic acid (Comparative Example 5), acetic acid (Comparative Example 6), or L-cysteine (Comparative Example 7) as a reducing agent.

In Comparative Example 4, although the reducibility was sufficient, the fused state of the particles of the conductive film was insufficient, and a conductive film having excellent conductivity could not be obtained. It is presumed that disproportionation of the reducing agent did not proceed efficiently during the drying process of the coating film because the boiling point of formic acid is low.

In Comparative Examples 5 and 6, the conductive film having excellent conductivity could not be obtained, probably because the reducing power was insufficient.

In Comparative Example 7, although the reducibility was sufficient and disproportionation of the reducing agent in the coating film was also progressing, L-cysteine consumed in the reduction was changed to a poorly soluble crystal, and in the coating film Since the copper particles were deposited, the copper particles could not contact effectively, and the fused state of the conductive film was insufficient, and a coating film excellent in conductivity could not be obtained.

11 substrate 12 coating film 13 drying film 14 lower layer (conductive film)
15 upper layer 16 interface 17 conductive film surface

Claims

Conductive film containing copper particles, reductone and at least one reducing agent selected from the group consisting of hydroxycarboxylic acids having two or more carboxy groups and one or more hydroxy groups in the molecule, and a dispersion medium Applying a composition for coating on the surface of a substrate to form a coating film;
The coating is dried at a temperature of 150 ° C. or less under an oxidative atmosphere to form a lower layer substantially free of copper oxide on the substrate and an oxide of copper disposed on the lower layer Obtaining a dried film comprising an upper layer comprising
And a peeling step of removing the upper layer from the dry film to obtain a conductive film.
(111) peak of Cu 2 O by X-ray diffraction method, the detected in the upper layer, the not detected in the lower, the production method of the conductive film of claim 1.
The method for producing a conductive film according to claim 1, wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, an ascorbic acid derivative and citric acid.
The method for producing a conductive film according to any one of claims 1 to 3, wherein an average particle diameter of the copper particles is in a range of 25 to 1500 nm.
The method for producing a conductive film according to any one of claims 1 to 4, further comprising a heating step of heating the conductive film at a temperature of more than 150 属 C and 190 属 C or less after the peeling step.
The method for producing a conductive film according to any one of claims 1 to 5, wherein the temperature of the drying step is 125 ° C or less.
The method for producing a conductive film according to any one of claims 1 to 6, wherein the composition for forming a conductive film does not contain a binder.
The method for producing a conductive film according to any one of claims 1 to 7, wherein the ratio of the mass of the copper particles to the mass of the reducing agent is 90 to 99 mass%.
A conductive film comprising copper and at least one reducing agent selected from the group consisting of reductone and a hydroxycarboxylic acid having two or more carboxy groups and one or more hydroxy groups in the molecule,
The electrically conductive film whose content of the said copper is 90 mass% or more with respect to the total mass of the said electrically conductive film.
The conductive film according to claim 9, wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, an ascorbic acid derivative and citric acid.
The electrically conductive film of Claim 9 or 10 which does not contain a binder.
The conductive film according to any one of claims 9 to 11, wherein the (111) peak of Cu 2 O by X-ray diffraction method is not detected.