TWI889022B - Conductive film forming method - Google Patents

Abstract

The present invention provides a conductive composition and a conductive film forming method for forming a conductive film with high electromagnetic shielding effect at low cost. The conductive composition exhibits conductivity after firing. The conductive composition contains copper nanoparticles, a liquid dispersion medium, a dispersant, and a thermosetting organic matrix. The dispersant is a polymer compound containing nitrogen atoms or phosphorus atoms. The organic matrix is composed of a liquid epoxy resin and a hardener for hardening the epoxy resin. The hardener is an alkaline nitrogen-containing compound. In the conductive film forming method, firing is performed in a formic acid environment or immersion in a formic acid aqueous solution before firing.

Description

Conductive film forming method

The present invention relates to a conductive composition for forming a conductive film suitable for electromagnetic shielding of electronic devices and a conductive film forming method using the conductive composition.

As electronic devices have become thinner and smaller in recent years, the mounting density of electronic parts has increased. Electronic devices emit unwanted radiation noise that can cause malfunctions, so as the mounting density of electronic parts increases, malfunctions caused by unwanted radiation noise (electromagnetic interference) may occur in other electronic devices or in electronic devices. In order to prevent such malfunctions, electromagnetic shielding (electromagnetic wave shielding, EMI shielding) is used to shield the unwanted radiation noise.

In the past, metal cans were used as electromagnetic shields. Metal cans are configured to cover three-dimensional objects that are the source of unwanted radiation noise. However, the use of metal cans is contrary to the lightweighting of electronic devices. In addition, metal cans have gaps that allow unwanted radiation noise to leak out. In addition, because the source of unwanted radiation noise needs to be concentrated in the area covered by the metal can, the design freedom of electronic devices is reduced.

In addition, a method of applying a conductive EMI shielding composition containing conductive particles on a source of unwanted radiation noise as an electromagnetic shield is known (see patent document 1). It is described that the conductive EMI shielding composition can be implemented with the conductive microparticles being silver particles (Examples 1 to 9 of the same document) or silver-coated copper particles (Example 10 of the same document). Silver is suitable for electromagnetic shielding because of its low resistivity, but it is expensive.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2017-520903

The present invention solves the above-mentioned problems and aims to provide a conductive composition and a conductive film forming method for forming a conductive film with high electromagnetic shielding effect at low cost.

The conductive composition of the present invention is conductive after firing, and is characterized by: containing copper nanoparticles, liquid dispersion medium, a dispersant for dispersing the copper nanoparticles in the dispersion medium, and a thermosetting organic matrix, wherein the dispersant is a polymer compound containing nitrogen atoms or phosphorus atoms, and the organic matrix is composed of a liquid epoxy resin and a hardener for hardening the epoxy resin, and the hardener is an alkaline nitrogen-containing compound.

In the conductive composition, for example, the dispersant is a branched polyester or a phosphate polyester having an amine.

In the conductive composition, the aforementioned hardener is preferably an amine.

In the conductive composition, for example, the curing agent is selected from the group consisting of imidazole derivatives, modified amines and phenolic aromatic amines.

The conductive film forming method of the present invention is a method for forming a conductive film on the surface of a target object, which is characterized by having the following steps: forming a liquid film composed of the conductive composition on the surface of the target object; drying the liquid film to form a particle film; and sintering the particle film in a formic acid environment to form a conductive film and harden the epoxy resin.

The conductive film forming method of the present invention is a method for forming a conductive film on the surface of a target object, which is characterized by having the following steps in sequence: forming a liquid film composed of the conductive composition on the surface of the target object; drying the liquid film to form a particle film; immersing the target object formed with the particle film in a formic acid aqueous solution; taking out the target object formed with the particle film from the formic acid aqueous solution and removing the liquid on the particle film; and firing the particle film in a passive environment to form a conductive film and harden the epoxy resin.

The conductive composition of the present invention uses copper nanoparticles as conductive particles, so the cost is lower than that of silver particles. Since copper has excellent conductivity, a conductive film with low resistivity can be formed by using the conductive composition. Since the conductive film is formed by copper nanoparticles, sintering is sufficient even at low temperatures and the resistivity is low. In addition, by using formic acid for sintering, the surface oxide film of the copper nanoparticles is reduced by formic acid and the resistivity of the conductive film formed is low. In addition, formic acid is used to promote the decomposition reaction of the dispersant and the resistivity of the conductive film formed is even lower. The surface of the conductive film is less affected by the epoxy resin due to formic acid and the resistivity is even lower. Since the resistivity of the surface of the conductive film is low, even if the conductive film is thin, the electromagnetic shielding effect is high due to the reflection of electromagnetic waves at the interface with the air. Since the interface between the conductive film and the target is far away from the surface of the conductive film, it is not easy to react with formic acid, which can cure the epoxy resin and improve the adhesion of the conductive film.

1: Conductive film

2: Target object

3: Working surface

4: Liquid film

5: Particle film

6: Formic acid aqueous solution

21: Top

22:Side

23: Bottom

30:Work board

Figures 1(a) to (d) are cross-sectional structural diagrams showing the conductive film forming method using the conductive composition of the first embodiment of the present invention in chronological order.

Figures 2(a) to (f) are cross-sectional structural diagrams showing the conductive film forming method using the conductive composition of the second embodiment of the present invention in chronological order.

(First implementation form)

The following describes the conductive composition of the first embodiment of the present invention. The conductive composition of the present invention is used for firing and exhibits conductivity after firing. The firing uses formic acid during or before firing. In the first embodiment, formic acid is used during firing (firing in a formic acid environment).

The conductive composition contains copper nanoparticles, a liquid dispersion medium, a dispersant, and a thermosetting organic matrix. The dispersant disperses the copper nanoparticles in the dispersion medium.

Dispersing medium solvent. Solvent is something that dissolves other substances, is liquid at room temperature and can evaporate.

Dispersants are polymer compounds containing nitrogen atoms or phosphorus atoms. Nitrogen atoms and phosphorus atoms are group 15 elements (nitrogen group elements) in the periodic table. They have negative charges different from carbon atoms and are highly reactive in organic molecular frameworks.

The organic matrix is composed of a liquid epoxy resin and a hardener. The epoxy resin is a thermosetting resin. The hardener hardens the epoxy resin. The hardener is an alkaline nitrogen-containing compound. The alkaline nitrogen-containing compound is an alkaline compound containing nitrogen atoms. The concentration of the hardener in the conductive composition can be set according to the type and concentration of the epoxy resin and the type of the hardener. In the present embodiment, the hardener is an amine. When the hardener is an amine, during the curing of the epoxy resin, the active hydrogen of the primary amine of the hardener reacts with the epoxy group to generate a secondary amine, the secondary amine reacts with the epoxy group to cure, and the generated tertiary amine polymerizes the epoxy group. The best amount of hardener mixed with epoxy resin is when the molar ratio of epoxy group and active hydrogen is equimolar.

The conductive composition is described in further detail below. Copper nanoparticles are nanometer-sized, that is, copper microparticles with a median diameter of more than 1nm and less than 1000nm.

烷、甲苯、庚烷、正十四烷。此外，分散媒可為多種溶劑之混合物。 Since the dispersing medium does not remain in the conductive film formed by firing the conductive composition, it does not affect the properties of the conductive film. Therefore, the dispersing medium is not limited to a specific solvent as long as it can disperse the copper nanoparticles therein and dissolve the organic matrix. In the present embodiment, the dispersing medium is, for example, cyclohexanone. Cyclohexanone is a polar aprotic solvent. The dispersing medium can be a polar aprotic solvent other than cyclohexanone, a polar protic solvent, or a non-polar solvent. Polar aprotic solvents are, for example, butyl acetate, N,N-dimethylformamide, acetone, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, tetrahydrofuran, α-terpineol, and N-methyl-2-pyrrolidone. Polar protic solvents include isopropanol and ethanol. Nonpolar solvents include cyclohexane, diethyl ether, 1,4-dihydroquinone,

In addition, the dispersion medium may be a mixture of various solvents.

In this embodiment, the dispersant is a branched polyester or a phosphate polyester having an amine. The amine has a nitrogen atom. The branched polyester is a polyester having a branched structure in the molecule. The phosphate polyester has a phosphorus atom (nitrogen group element).

In this embodiment, the hardener is an imidazole derivative or a phenolic aromatic amine. Imidazole derivatives and phenolic aromatic amines are amines, i.e., alkaline nitrogen-containing compounds.

The following describes a method for forming a conductive film using the conductive composition with reference to FIGS. 1(a) to (d). The conductive film forming method is a method for forming a conductive film on the surface of a target object. The target object is an electronic device in this embodiment. The surface of the electronic device is, for example, a molding resin.

First, as shown in FIG1(a), the target 2 is placed on the working surface 3. The target 2 is generally a three-dimensional object in the case of an electronic device. In the present embodiment, the target 2 has a roughly rectangular shape and has a top surface 21, a plurality of side surfaces 22, and a bottom surface 23. The top surface 21 is a horizontal surface and each side surface 22 is a roughly vertical surface. Because the electronic device is mounted on a printed circuit board, etc., a conductive film is usually not formed on the bottom surface 23 of the target 2 (electronic device). In addition, the shape of the target 2 is not limited to a rectangular parallelepiped, and can be, for example, a cylinder and a hemisphere. In addition, the target 2 is not limited to a three-dimensional object, and can be a planar object.

Next, as shown in FIG. 1( b ), the conductive composition is used to form a liquid film 4 composed of the conductive composition on the surface of the target 2. Since the conductive composition contains an epoxy resin as an adhesive resin, the liquid film 4 adheres to the surface of the target 2. In the present embodiment, the liquid film 4 is formed on the surface of the target 2 by spraying. Spraying is performed using, for example, a spray gun. When the liquid film 4 is formed by spraying, the thickness of the liquid film 4 on the side surface 22 can be controlled more easily by adjusting the spray angle and the nozzle position than by other coating methods such as sputtering. The spray angle and nozzle position are adjusted so that the film thickness of the liquid film 4 on the top surface 21 and each side surface 22 is roughly the same.

Next, the liquid film 4 is dried to form a particle film 5 as shown in FIG1(c). By drying the liquid film 4, the dispersion medium in the conductive composition evaporates, and the copper nanoparticles condense to form a particle film 5 as an aggregate. The particle film 5 is mainly composed of copper nanoparticles and includes a dispersant, an epoxy resin, and a hardener. Because the particle film 5 includes an epoxy resin, it is attached to the surface of the target 2.

Next, as shown in FIG. 1( d ), the particle film 5 is fired in a formic acid environment to form a conductive film 1 . The firing of the particle film 5 is performed by thermal firing by heating and, for example, using a formic acid reflow device. During the firing, the copper nanoparticles in the particle film 5 are sintered to form a conductive film 1 and are in close contact with the target 2 . The conductive film 1 has conductivity. In addition, by the heat of the firing, the epoxy resin in the particle film 5 reacts chemically with the hardener and the epoxy resin is hardened. By hardening the epoxy resin, the adhesion of the conductive film 1 to the target 2 is improved.

Thus, in the first embodiment, the conductive composition is used for the firing using formic acid and exhibits conductivity after firing.

As described above, according to the conductive composition of this embodiment, copper nanoparticles are used as conductive particles, so the cost is lower than that of silver particles. Since copper has excellent conductivity, the conductive film 1 formed by using the conductive composition has low resistivity and high electromagnetic shielding effect. Even if the conductive film 1 is thin, the electromagnetic shielding effect is high due to the reflection of electromagnetic waves at the interface with the air.

In the conductive film forming method using the conductive composition, since the particle film 5 contains copper nanoparticles, the temperature required for firing is low and the firing time is short. Therefore, the impact on the target object 2 (electronic devices, etc.) caused by firing is small. In addition, since the conductive film 1 is formed of copper nanoparticles, firing is fully performed even at low temperatures, the resistivity is low, and the electromagnetic shielding effect is high.

The outermost surface of the copper nanoparticles in the particle film 5 is oxidized by oxygen contained in the atmosphere and has a surface oxide film. In the conductive film forming method, by firing the particle film 5 in a formic acid environment, the surface oxide film of the copper nanoparticles is reduced by formic acid, and the conductive film 1 formed has a low resistivity and a high electromagnetic shielding effect.

Until a liquid film composed of the conductive composition is formed on the surface of the target 2, a dispersant in the conductive composition is required to disperse the copper nanoparticles. However, the dispersant remaining in the conductive film 1 will increase the resistance. The dispersant is a polymer compound containing nitrogen atoms or phosphorus atoms. The negative charge of nitrogen atoms and phosphorus atoms is different from that of carbon atoms and is highly reactive in the organic molecular skeleton. Therefore, when fired in a formic acid environment, the decomposition reaction of the dispersant is promoted. Because the dispersant decomposes, the resistivity of the formed conductive film 1 is low and the electromagnetic shielding effect is high. Even if the conductive film 1 is thin, the electromagnetic shielding effect is high due to the reflection of electromagnetic waves at the interface with the air.

In this embodiment, the dispersant is a branched polyester or a phosphate polyester having an amine. When the dispersant is a branched polyester having an amine, since the amine is alkaline, it is easy to react with acidic formic acid, and thus the decomposition can be promoted by formic acid. When the dispersant is a phosphate polyester, since the phosphate group is an acid group, it is impossible to understand its relationship with formic acid by only using acid-base reaction. The low resistivity of the formed conductive film 1 is difficult to predict, and is discovered by the inventor of this application after many experiments.

The epoxy resin in the conductive composition hardens during firing to improve the adhesion of the conductive film 1. However, since the hardened epoxy resin in the conductive film 1 is an insulator, the resistivity of the conductive film 1 increases. Therefore, the specific value of the concentration of the liquid epoxy resin in the conductive composition should be set based on experiments to take into account both the adhesion and low resistivity of the conductive film 1.

However, as shown in the experimental results described below, even if the concentration of the epoxy resin is slightly higher than that which satisfies both the adhesion and resistivity of the conductive film 1, it has almost no adverse effect on the resistivity of the conductive film 1 (see Examples 1 and 2, Examples 4 and 5, Examples 6 and 7, etc.). On the contrary, even if the concentration of the epoxy resin is slightly lower than that which satisfies both the adhesion and resistivity of the conductive film 1, it has little effect on the resistivity of the conductive film 1 (see Examples 1 and 3).

Since the electronic device (target 2) that radiates the unwanted radiation noise operates at a high frequency, the unwanted radiation noise is a high-frequency electromagnetic wave. Generally speaking, electromagnetic waves propagating in a medium are reflected at the interface between different media due to the difference in impedance of the medium. The conductive film 1 is formed on the surface of the target 2 and exists in the air. Since air is an excellent insulator, the impedance is very high. The conductive film 1 has very low impedance because it is conductive. The impedance of the surface of the target 2 is higher than that of the conductive film 1. The electromagnetic waves radiated by the target 2 are reflected at the interface between the target 2 and the conductive film 1 due to the difference in impedance, a part of them is emitted into the conductive film 1, attenuated in the conductive film 1, reflected at the interface between the conductive film 1 and the air, and a part of them is emitted into the air. The electromagnetic wave radiated from the outside to the target 2 is reflected at the interface between the air and the conductive film 1 due to the impedance difference, a part of it is incident on the conductive film 1, attenuated inside the conductive film 1, and a part of it is reflected at the interface between the conductive film 1 and the target 2 and a part of it is incident on the target 2. Among these reflection and attenuation phenomena, the reflection obtained by utilizing the large impedance difference between the conductive film 1 and the air contributes greatly to the shielding of high-frequency electromagnetic waves. Therefore, the higher the conductivity of the surface of the conductive film 1, the greater the impedance difference at the interface with the air, and the higher the electromagnetic shielding effect of shielding useless radiation noise.

It is inferred from the experimental results that during the firing in a formic acid environment, near the surface of the particle film 5 or the conductive film 1, the formic acid as an acid decomposes to become a hardener of the alkaline nitrogen-containing compound and hinders the curing of the epoxy resin. In addition, because of its strong acidity, formic acid causes the epoxy ring to open. That is, during the firing, the sintering of the copper nanoparticles, the curing of the epoxy resin, the decomposition of the hardener, and the opening of the epoxy resin proceed simultaneously. Due to the decomposition of the hardener and the opening of the epoxy resin, the influence of the epoxy resin is small near the surface of the conductive film 1 and the resistivity is low. Since the resistivity of the conductive film 1 is measured by making the measuring electrode contact the surface of the conductive film 1, a low resistivity is measured. Since the surface of the conductive film 1 has a low resistivity, the electromagnetic shielding effect against high-frequency useless radiation noise is high due to the electromagnetic wave reflection at the interface with the air. Since the interface between the conductive film 1 and the target 2 is far away from the surface of the conductive film 1, it is not easy to react with formic acid, and the epoxy resin can be cured and the adhesion of the conductive film can be improved.

(Second implementation form)

The following describes the conductive composition of the second embodiment of the present invention. The conductive composition of the second embodiment has the same composition as the first embodiment. In the following description, the same symbols are given to the same parts as the first embodiment. The detailed description of the same parts as the first embodiment is omitted.

The conductive composition is used for firing and exhibits conductivity after firing. In the second embodiment, formic acid is used before firing (immersion in a formic acid aqueous solution before firing).

The conductive composition contains copper nanoparticles, a liquid dispersion medium, a dispersant, and a thermosetting organic matrix. The dispersant disperses the copper nanoparticles in the dispersion medium.

Dispersing medium is organic solvent.

Dispersants are high molecular weight compounds containing nitrogen atoms or phosphorus atoms (nitrogen group elements).

The organic matrix is composed of a liquid epoxy resin and a hardener. The hardener hardens the epoxy resin. The hardener hardens the epoxy resin. The hardener is an alkaline nitrogen-containing compound.

烷、甲苯、庚烷、正十四烷。此外，分散媒可為多種溶劑之混合物。 Since the dispersing medium does not remain in the conductive film formed by firing the conductive composition, it does not affect the properties of the conductive film. Therefore, the dispersing medium can disperse the copper nanoparticles therein and is not limited to a specific solvent as long as it can dissolve the organic matrix. In this embodiment, the dispersing medium is, for example, cyclohexanone. Cyclohexanone is a polar aprotic solvent. The dispersing medium can be a polar aprotic solvent other than cyclohexanone, a polar protic solvent, or a non-polar solvent. Polar aprotic solvents are, for example, butyl acetate, N,N-dimethylformamide, acetone, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, tetrahydrofuran, α-terpineol, and N-methyl-2-pyrrolidone. Polar protic solvents include isopropanol and ethanol. Nonpolar solvents include cyclohexane, diethyl ether, 1,4-dihydroquinone,

In addition, the dispersion medium may be a mixture of various solvents.

In this embodiment, the dispersant is a branched polyester or a phosphate polyester having an amine. The amine has a nitrogen atom. The phosphate polyester has a phosphorus atom (a nitrogen group element).

In this embodiment, the hardener is selected from the group consisting of imidazole derivatives, modified amines and phenolic aromatic amines. These hardeners are all amines, i.e., alkaline nitrogen-containing compounds.

The following describes a method for forming a conductive film using the conductive composition with reference to FIGS. 2(a) to (f). The conductive film forming method is a method for forming a conductive film on the surface of a target object. In this embodiment, the target object is an electronic device.

First, place the target object 2 on the working surface 3 as shown in FIG2(a). In this embodiment, the working surface 3 is the top surface of the working plate 30.

Next, as shown in FIG. 2( b ), a liquid film 4 composed of the conductive composition of the second embodiment is formed on the surface of the target 2. Since the conductive composition contains an epoxy resin as an adhesive resin, the liquid film 4 adheres to the surface of the target 2. In this embodiment, the liquid film 4 is formed on the surface of the target 2 by spraying. Spraying is performed using, for example, a spray gun. When the liquid film 4 is formed by spraying, the thickness of the liquid film 4 on the side surface 22 can be controlled more easily by adjusting the spray angle and the nozzle position than by other coating methods such as sputtering. The spray angle and nozzle position are adjusted so that the film thickness of the liquid film 4 on the top surface 21 and each side surface 22 is roughly the same.

Next, the liquid film 4 is dried to form a particle film 5 as shown in FIG2(c). By drying the liquid film 4, the dispersion medium in the conductive composition evaporates, and the copper nanoparticles condense to form a particle film 5 as an aggregate. The particle film 5 is mainly composed of copper nanoparticles and includes a dispersant, an epoxy resin, and a hardener. Because the particle film 5 includes an epoxy resin, it is attached to the surface of the target 2.

Next, as shown in FIG2(d), the target 2 formed with the particle film 5 is immersed in the formic acid aqueous solution 6. The formic acid aqueous solution 6 dissolves the dispersant contained in the particle film 5.

Next, as shown in FIG. 2(e), the target 2 formed with the particle film 5 is taken out from the formic acid aqueous solution 6 and the liquid on the particle film 5 is removed. In this embodiment, the liquid on the particle film 5 is removed by blowing. The means of removing the liquid on the particle film 5 is not limited to blowing. For example, acceleration such as centrifugal force can be applied to the target 2 to remove the liquid on the particle film 5. In addition, the liquid to be removed is a formic acid aqueous solution in which a dispersant is dissolved. In addition, even if the particle film 5 is dried, only the water in the liquid is evaporated, so the dispersant in the liquid remains and the liquid cannot be removed.

Next, as shown in FIG. 2(f), the particle film 5 is fired in a passive environment to form a conductive film 1. The firing of the particle film 5 is thermal firing by heating. The passive environment is, for example, a nitrogen environment. During the firing, the copper nanoparticles in the particle film 5 are sintered to form a conductive film 1 and are in close contact with the target 2. The conductive film 1 has conductivity. In addition, by the heat of the firing, the epoxy resin in the particle film 5 reacts chemically with the hardener and the epoxy resin is hardened. By hardening the epoxy resin, the adhesion of the conductive film 1 to the target 2 is improved.

Thus, in the second embodiment, the conductive composition is used for firing with formic acid before firing and exhibits conductivity after firing.

As described above, according to the conductive composition of this embodiment, copper nanoparticles are used as conductive particles, so the cost is lower than that of silver particles. Since copper has excellent conductivity, the conductive film 1 formed by using the conductive composition has low resistivity and high electromagnetic shielding effect.

In the conductive film forming method using the conductive composition, the particle film 5 contains copper nanoparticles, so the temperature required for firing is low and the firing time is short. Therefore, the impact on the target 2 (electronic devices, etc.) caused by firing is small. In addition, because the conductive film 1 is formed of copper nanoparticles, firing is fully performed even at low temperatures, the resistivity is low, and the electromagnetic shielding effect is high.

The outermost surface of the copper nanoparticles in the particle film 5 is oxidized by oxygen contained in the atmosphere and has a surface oxide film. In the conductive film forming method, since the particle film 5 is immersed in a formic acid aqueous solution 6 before firing, the surface oxide film of the copper nanoparticles is reduced by formic acid, and the formed conductive film 1 has a low resistivity and a high electromagnetic shielding effect.

Until a liquid film composed of the conductive composition is formed on the surface of the target 2, the dispersant in the conductive composition is required to disperse the copper nanoparticles. However, the dispersant remaining in the conductive film 1 will increase the resistance. In this embodiment, the dispersant is a branched polyester or a phosphate polyester having an amine.

When the dispersant is a branched polyester having amine, since the amine is alkaline, it easily reacts with acidic formic acid and is therefore easily dissolved in the formic acid aqueous solution 6. Since the dispersant is dissolved from the conductive composition, the formed conductive film 1 has a low resistivity and a high electromagnetic shielding effect. Even if the conductive film 1 is thin, the electromagnetic shielding effect is high due to the reflection of electromagnetic waves at the interface with the air.

When the dispersant is a phosphate polyester, since the phosphate group is an acid group, it is impossible to understand its relationship with the formic acid aqueous solution 6 by only using the acid-base reaction. The low resistivity of the formed conductive film 1 is difficult to predict, and was discovered by the inventor of this application after many experiments.

When formic acid reacts with the alkaline nitrogen-containing compound of the hardener to form a salt, the dissociation constant of phosphoric acid is greater than that of formic acid, so the formic acid salt dissociates the formic acid to form the phosphoric acid salt. Therefore, it is considered that there is a possibility that the dispersant is easily dissolved from the conductive composition into the formic acid aqueous solution 6. In addition, this inference is a statement used to explain the experimental results and does not limit the technical scope of the invention of this application.

The same inference is made about the epoxy resin in the conductive composition of the second embodiment as in the first embodiment. By immersing the particle film 5 in a formic acid aqueous solution before firing, the formic acid as an acid decomposes near the surface of the particle film 5 to serve as a hardener for the alkaline nitrogen-containing compound. In addition, since formic acid is highly acidic, it causes the epoxy ring to open. Therefore, after firing, near the surface of the conductive film 1, the influence of the epoxy resin is small and the resistivity is low. Since the resistivity of the conductive film 1 is measured by bringing the measuring electrode into contact with the surface of the conductive film 1, a low resistivity is measured. Since the surface layer of the conductive film 1 has a low resistivity, the electromagnetic shielding effect against high-frequency unnecessary radiation noise is high due to the reflection of electromagnetic waves at the interface with the air. Since the interface between the particle film 5 and the target 2 is far away from the surface of the particle film 5, it is not easy to react with formic acid, so the epoxy resin can be hardened and the adhesion of the conductive film 1 can be improved.

A conductive composition as the first embodiment of the present invention and a conductive composition for comparison were prepared and used to attempt to form a conductive film. The conductive composition was prepared by the following method. Spherical copper particles with a median diameter of 40 to 50 nm were used as copper nanoparticles. According to each experimental condition, the weighed dispersant, epoxy resin and hardener were dissolved in a dispersion medium and the copper nanoparticles were dispersed therein. Then, the prepared conductive composition was sprayed on the surface of the target object. Then, the liquid film of the conductive composition was dried to form a particle film. Then, the particle film was fired in a formic acid environment. Then, the adhesion and volume resistivity of the formed conductive film to the target object were evaluated.

The evaluation of adhesion is carried out according to ASTM specification D2259. This specification is to cut 6 vertical strips × 6 horizontal strips in the conductive film 1 to make 25 blocks of 2mm × 2mm in size, conduct a tape peeling test and assign 6 levels from "0B" to "5B" according to the proportion of the peeling area.

[Implementation Example 1]

The dispersion medium is cyclohexanone (the same in Examples 1 to 23 and Comparative Examples 1 to 3). The concentration of the copper nanoparticles relative to the entire conductive composition (hereinafter, the same in terms of mass%) is 37.4 mass%. The dispersant is a branched polyester having amine (manufactured by BYK, trade name "DISPERBYK (registered trademark)-2155") and its concentration is 1.5 mass%. The epoxy resin is an epoxy resin that is liquid at room temperature (manufactured by Mitsubishi Chemical Co., Ltd., trade name "YX7105") and its concentration is 2.8 mass%. The curing agent is tris-dimethylaminomethylphenol (manufactured by Mitsubishi Chemical Co., Ltd., trade name "jER CURE (registered trademark) 3010") which is a phenolic aromatic amine, and its concentration is 3.63% by mass. The firing temperature is 150°C (the same in Examples 1 to 39 and Comparative Examples 1 to 3).

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity (volume resistivity) of the conductive film is 2.0×10 ^-4 Ω. cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 2]

The concentration of copper nanoparticles is 35.9 mass%, which is approximately the same as that of Example 1. The dispersant is the same as that of Example 1 and its concentration is 1.4 mass%, which is approximately the same as that of Example 1. The epoxy resin is the same as that of Example 1 and its concentration is 4.5 mass%, which is higher than that of Example 1. The hardener is the same as that of Example 1 and its concentration is 5.79 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 1.1×10 ^-4 Ω．cm.

That is, in Example 2, although the concentration of epoxy resin was increased to 1.6 times that of Example 1, the resistivity of the formed conductive film did not increase. This is an unexpected result at first glance, but as mentioned above, it is speculated that the surface of the conductive film is not easily affected by the epoxy resin due to the action of formic acid. In addition, a slight decrease in resistivity is considered to be within the range of variation.

[Implementation Example 3]

The concentration of copper nanoparticles is 39.1 mass%, which is approximately the same as that of Example 1. The dispersant is the same as that of Example 1 and its concentration is 1.6 mass%, which is approximately the same as that of Example 1. The epoxy resin is the same as that of Example 1 and its concentration is 1.0 mass%, which is lower than that of Example 1. The hardener is the same as that of Example 1 and its concentration is 1.26 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, the peeled pieces are grade 3B of ASTM specification D2259. Grade 3B means the peeled pieces are in the range of 5% to 15%. When the conductive film is actually used as an electromagnetic shield, it is not finely cut, so if there is such a degree of adhesion, it is likely to be used. The resistivity of the conductive film is 1.7×10 ^-4 Ω. cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, in Example 3, the concentration of epoxy resin is significantly reduced compared to Example 1, resulting in a decrease in the adhesion of the conductive film. In addition, in Example 3, although the concentration of epoxy resin is reduced to 0.36 times that of Example 1, the resistivity of the formed conductive film is only reduced to 0.85 times. Because the resistivity of the conductive film is measured independently from the peeling test, the resistivity does not increase due to the partial peeling of the block. As mentioned above, it is speculated that the surface of the conductive film is not easily affected by the epoxy resin due to the action of formic acid.

(Comparative example 1)

The following low concentration experiment was conducted as a comparative example, that is, the concentration of the epoxy resin was made lower than that of Example 3, so that the conductive composition could not be said to substantially contain the epoxy resin. The concentration of the copper nanoparticles was 39.5 mass%, which was approximately the same as that of Example 3. The dispersant was the same as that of Examples 1 to 3 and its concentration was 1.6 mass%, which was the same as that of Example 3. The epoxy resin was the same as that of Examples 1 to 3 and its concentration was 0.5 mass%, which was lower than that of Example 3. The hardener was the same as that of Examples 1 to 3 and its concentration was 0.64 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, the peeled pieces are grade 0B of ASTM specification D2259. Grade 0B means that the peeled pieces exceed 65%.

That is, it was confirmed that the conductive film cannot be adhered to at a low concentration such that the conductive composition cannot be said to substantially contain epoxy resin. In addition, from the results of Comparative Example 1, it can be seen that the conductive film cannot be adhered to even if the concentration of epoxy resin is completely 0. The specific concentration value of epoxy resin as an insulator is preferably set to take into account both the adhesion between the conductive film obtained by epoxy resin and the target object and the electromagnetic shielding effect obtained by low resistivity (design matter).

[Implementation Example 4]

The concentration of copper nanoparticles is 38.4 mass%, which is approximately the same as that of Example 1. The dispersant is the same as that of Example 1 and its concentration is 1.5 mass%, which is approximately the same as that of Example 1. The epoxy resin is the same as that of Example 1 and its concentration is 2.9 mass%, which is approximately the same as that of Example 1. The hardener is an imidazole derivative (manufactured by Mitsubishi Chemical Co., Ltd., trade name "jER CURE (registered trademark) P200H50") and its concentration is 0.99 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 1.5×10 ^-3 Ω. cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even if the hardener is replaced with an imidazole derivative, a conductive film suitable for electromagnetic shielding of electronic devices can be formed.

[Implementation Example 5]

The concentration of copper nanoparticles is 37.5 mass%, which is approximately the same as that of Example 4. The dispersant is the same as that of Example 4 and its concentration is 1.5 mass%, which is the same as that of Example 4. The epoxy resin is the same as that of Example 4 and its concentration is 4.7 mass%, which is higher than that of Example 4. The hardener is the same as that of Example 4 and its concentration is 1.61 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 5.8×10 ^-4 Ω．cm.

That is, in Example 5, although the concentration of epoxy resin is increased to 1.6 times that of Example 4, the resistivity of the formed conductive film does not increase. That is, the tendency of Example 5 relative to Example 4 is the same as the tendency of Example 2 relative to Example 1. It is speculated that this is because the surface of the conductive film is not easily affected by the epoxy resin due to the action of formic acid. In addition, a slight decrease in resistivity is considered to be a range of variation, but it is also believed that the higher the concentration of the reactant, the higher the reaction rate.

[Implementation Example 6]

The concentration of copper nanoparticles is 37.9 mass%, which is approximately the same as that of Examples 1 and 4. The dispersant is the same as that of Examples 1 and 4 and its concentration is 1.5 mass%, which is the same as that of Examples 1 and 4. The epoxy resin is a liquid epoxy resin at room temperature (manufactured by Mitsubishi Chemical Co., Ltd., trade name "828") and its concentration is 2.8 mass%, which is the same as that of Example 1. The hardener is the same as that of Example 4 and its concentration is 2.48 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 3.7×10 ^-3 Ω. cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even if different epoxy resins are used, a conductive film suitable for electromagnetic shielding of electronic devices can be formed.

[Implementation Example 7]

The concentration of copper nanoparticles is 36.6 mass%, which is approximately the same as that of Example 6. The dispersant is the same as that of Example 6 and its concentration is 1.5 mass%, which is the same as that of Example 6. The epoxy resin is the same as that of Example 6 and its concentration is 4.6 mass%, which is higher than that of Example 6. The hardener is the same as that of Example 6 and its concentration is 3.99 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 2.7×10 ^-3 Ω．cm.

That is, in Example 7, although the concentration of epoxy resin is increased to 1.6 times that of Example 6, the resistivity of the formed conductive film does not increase. That is, the inclination of Example 7 relative to Example 6 is the same as the inclination of Example 2 relative to Example 1. It is speculated that this is because the surface of the conductive film is not easily affected by the epoxy resin due to the action of formic acid. In addition, a slight decrease in resistivity is considered as a range of variation.

[Implementation Example 8]

The concentration of copper nanoparticles is 37.8 mass % which is approximately the same as that of Examples 1 and 6. The dispersant is the same as that of Examples 1 and 6 and its concentration is 1.5 mass % which is the same as that of Examples 1 and 6. The epoxy resin is a phenol novolac type epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., trade name "152") which is liquid at room temperature and its concentration is 2.8 mass % which is the same as that of Examples 1 and 6. The hardener is the same as that of Example 6 and its concentration is 2.67 mass %.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 5.5×10 ^-3 Ω. cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even if different types of epoxy resins are used, a conductive film suitable for electromagnetic shielding of electronic devices can be formed.

[Implementation Example 9]

The concentration of copper nanoparticles is 36.5 mass%, which is approximately the same as that of Example 8. The dispersant is the same as that of Example 8 and its concentration is 1.5 mass%, which is the same as that of Example 8. The epoxy resin is the same as that of Example 8 and its concentration is 4.6 mass%, which is higher than that of Example 8. The hardener is the same as that of Example 8 and its concentration is 4.30 mass%.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 6.2×10 ^-3 Ω．cm.

That is, in Example 9, although the concentration of epoxy resin was increased to 1.6 times that of Example 8, the resistivity of the formed conductive film was only increased to 1.1 times. It is speculated that the reason is that the surface of the conductive film is not easily affected by the epoxy resin due to the action of formic acid.

(Comparative example 2)

As a comparative example, phenol resin was used instead of epoxy resin. No hardener is required in phenol resin. The concentration of copper nanoparticles is 40 mass % which is approximately the same as that in Example 1. The dispersant is the same as that in Example 1 and its concentration is 1.6 mass % which is approximately the same as that in Example 1. Phenol resin is used as the thermosetting resin and its concentration is 3 mass % which is approximately the same as that in Example 1.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, the peeled pieces are grade 0B of ASTM specification D2259. Grade 0B means that the peeled pieces exceed 65%.

That is, when the conductive composition does not substantially contain epoxy resin but contains phenol resin instead, the adhesion of the conductive film cannot be obtained.

A conductive composition as the second embodiment of the present invention and a conductive composition for comparison are prepared and used to attempt to form a conductive film. The conductive composition is prepared by the same method as the first embodiment. The target object is the same as the first embodiment. Then, the prepared conductive composition is sprayed on the surface of the target object. Then, the liquid film of the conductive composition is dried at 80°C for 1 minute using a heating plate to form a particle film. Then, the target object with the particle film formed is immersed in a 3 mass% formic acid aqueous solution. Then, the target object with the particle film formed is taken out from the formic acid aqueous solution and the liquid on the particle film is removed by blowing with a blower. Then, the particle film is fired in a nitrogen environment. Next, evaluate the adhesion and volume resistivity of the formed conductive film to the target object.

[Example 10]

The concentration of copper nanoparticles is 38 mass % which is approximately the same as that of Example 1 (hereinafter, the same also applies to Examples other than Example 18 and Comparative Example 3). The dispersant is a phosphate polyester (manufactured by BYK, trade name "DISPERBYK (registered trademark) -111") and its concentration is 2 mass % (hereinafter, the same dispersant in Examples 11 to 15, 2 mass %). The epoxy resin is the same as that of Example 1 and its concentration is 3 mass % which is approximately the same as that of Example 1. The hardener is an imidazole derivative (manufactured by ADEKA Corporation, trade name "ADEAKHARDENER (registered trademark) EH-2021") and its concentration is 1 mass %.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, there is no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 25μΩ.cm (25×10 ^-6 Ω.cm) and is a low value suitable for electromagnetic shielding of electronic devices.

That is, the particle film is immersed in a formic acid aqueous solution before firing, thereby forming a conductive film with low resistivity. The resistivity is lower than that of Examples 1 to 9 (first embodiment) fired in a formic acid environment.

[Implementation Example 11]

The epoxy resin is the same as that in Example 10 and has the same concentration. The hardener is a modified amine (manufactured by T&K TOKA Co., Ltd., trade name "FUJICURE (registered trademark) 7001") and its concentration is 1 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 20μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even when a modified amine is used as a hardener, a conductive film suitable for electromagnetic shielding of electronic devices is formed.

[Implementation Example 12]

The epoxy resin is the same as that in Example 10 and has the same concentration. The hardener is different from that in Example 10 and is the same imidazole derivative as in Examples 4 to 9 and has a concentration of 1 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 51μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even when different imidazole derivatives are used as hardeners, a conductive film suitable for electromagnetic shielding of electronic devices can be formed.

[Implementation Example 13]

The epoxy resin is different from Examples 10 to 12, and is the same as Examples 6 and 7, and its concentration is 3% by mass. The hardener is the same imidazole derivative as in Example 10, and its concentration is 3% by mass.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 94μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even if different epoxy resins are used, a conductive film suitable for electromagnetic shielding of electronic devices can be formed.

[Example 14]

The epoxy resin is the same as that in Example 13 and its concentration is 3% by mass, which is the same as that in Example 13. The hardener is the same modified amine as that in Example 11 and its concentration is 2% by mass.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 36μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 15]

The epoxy resin is the same as that in Examples 13 and 14 and its concentration is 3% by mass, which is the same as that in Examples 13 and 14. The hardener is the same imidazole derivative as that in Example 12 and its concentration is 2% by mass.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 222μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 16]

The dispersant is the same branched polyester as in Examples 1 to 9 and its concentration is 2 mass % (hereinafter, in Examples other than Example 18 and Comparative Example 3, the same dispersant is 2 mass %). The epoxy resin is the same as in Examples 13 to 15 and its concentration is 3 mass % as in Examples 13 to 15. The hardener is the same modified amine as in Example 14 and its concentration is 2 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 107μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even when branched polyester is used as a dispersant, a conductive film suitable for electromagnetic shielding of electronic devices can be formed.

[Example 17]

The epoxy resin is the same as that in Examples 10 to 12 and its concentration is 3 mass % (3 mass %) as that in Examples 10 to 12 (same epoxy resin in Examples 17 to 22 and Comparative Example 3). The hardener is the same imidazole derivative as that in Example 10 and its concentration is 1 mass % as that in Example 10.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 60μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 18]

The concentration of copper nanoparticles is 37% by mass, which is approximately the same as in Examples 16 and 17. The dispersant is the same branched polyester as in Examples 16 and 17 and its concentration is 1% by mass. The hardener is the same tris-dimethylaminomethylphenol as in Examples 1 to 3 and its concentration is 4% by mass.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 30μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

That is, even when 3,4-dimethylaminomethylphenol is used as a hardener in the second embodiment, a conductive film suitable for electromagnetic shielding of electronic devices is formed.

[Implementation Example 19]

The hardener is a modified amine (manufactured by T&K TOKA Co., Ltd., trade name "FUJICURE (registered trademark) FXR-1030") and its concentration is 1 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 72μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 20]

The hardener is a modified amine (manufactured by T&K TOKA Co., Ltd., trade name "FUJICURE (registered trademark) 7000") and its concentration is 1 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 65μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 21]

The hardener is the same modified amine as in Example 16 and its concentration is the same as in Example 16, 1 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 88μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 22]

The hardener is a modified amine (manufactured by Mitsubishi Chemical Co., Ltd., trade name "jER CURE (registered trademark) ST12") and its concentration is 2 mass %.

After firing, a conductive film is formed. There is no peeling block in the tape peeling test of the conductive film, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film is 110μΩ.cm, which is a low value suitable for electromagnetic shielding of electronic devices.

(Comparative example 3)

As a comparative example, a thiol was used instead of a hardener. A thiol is an organic compound having a sulfur atom. The hardener was 3-hydroxypropionate of thiol (manufactured by Mitsubishi Chemical Co., Ltd., trade name "jER CURE (registered trademark) QX40") and its concentration was 1 mass %.

After firing, a conductive film is formed. There is no peeled block in the tape peeling test of the conductive film (grade 5B of ASTM specification D2259). However, the resistivity of the conductive film is too high to be measured.

The hardener is not an amine, so it is speculated that the hardener in the particle film did not react with formic acid and the hardened epoxy resin remained in the entire conductive film, and the resistivity of the surface layer of the conductive film was not low.

[Example 23]

In Examples 1 to 9 of the aforementioned first embodiment, the dispersant is a polymer compound having nitrogen atoms (a nitrogen group element of the second period). The same experiment is conducted using a polymer compound having phosphorus atoms (a nitrogen group element of the third period) as a dispersant as an example of the first embodiment.

The dispersant is the same phosphate polyester as in Example 10 and its concentration is 1.5% by mass. Other experimental conditions (dispersant, concentration of copper nanoparticles, epoxy resin and its concentration, hardener and its concentration, firing temperature, etc.) are the same as in Example 1.

After firing, a conductive film was formed. In the tape peeling test of the conductive film, there was no peeling block, showing excellent adhesion (grade 5B of ASTM specification D2259). The resistivity of the conductive film was 2.0×10 ^-4 Ω. cm, which is the same low value as Example 1.

[Example 24]

In Examples 1 to 9 and 23 of the first embodiment, the dispersion medium is cyclohexanone (polar aprotic solvent). The dispersion medium can be used as long as it can disperse the copper nanoparticles and dissolve the organic matrix. Here, the dispersion medium is changed to conduct the same experiment as an example of the first embodiment.

The dispersion medium is cyclohexane. Cyclohexane is a non-polar solvent. Other experimental conditions (copper nanoparticle concentration, dispersant and its concentration, epoxy resin and its concentration, hardener and its concentration, firing temperature, etc.) are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.0×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 25]

The dispersion medium is butyl acetate. Butyl acetate is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.2×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 26]

The dispersion medium is diethyl ether. Diethyl ether is a non-polar solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.0×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 27]

烷。1,4-二

烷係無極性溶劑。除此以外之實驗條件與實施例1相同。 Dispersing medium 1,4-dimethoxy

1,4-Dihydrogen alkane

Alkanes are non-polar solvents. Other experimental conditions were the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.5×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 28]

The dispersion medium is toluene. Toluene is a non-polar solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.3×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 29]

The dispersion medium is heptane. Heptane is a non-polar solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.2×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 30]

The dispersion medium is n-tetradecane. n-tetradecane is a non-polar solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 4.0×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 31]

The dispersion medium is N,N-dimethylformamide. N,N-dimethylformamide is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.8×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 32]

The dispersion medium is acetone. Acetone is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, level 5B. The resistivity of the conductive film was 3.1×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 33]

The dispersion medium is propylene glycol monomethyl ether acetate (PGMA). Propylene glycol monomethyl ether acetate is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.7×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 34]

The dispersion medium is propylene glycol monomethyl ether (PM). Propylene glycol monomethyl ether is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.2×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 35]

The dispersion medium is tetrahydrofuran (THF). Tetrahydrofuran is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.9×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 36]

The dispersion medium is α-terpineol. α-terpineol is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.5×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Example 37]

The dispersion medium is N-methyl-2-pyrrolidone (NMP). N-methyl-2-pyrrolidone is a polar aprotic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.7×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 38]

The dispersion medium is isopropyl alcohol (2-propanol). Isopropyl alcohol is a polar protic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.3×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

[Implementation Example 39]

The dispersion medium is ethanol. Ethanol is a polar protic solvent. Other experimental conditions are the same as those in Example 1.

After firing, a conductive film was formed. The adhesion of the conductive film was the same as that of Example 1, Grade 5B. The resistivity of the conductive film was 3.5×10 ^-5 Ω·cm, which is a low value suitable for electromagnetic shielding of electronic devices.

In Examples 24 to 39 in which the dispersion medium is changed, non-polar solvents, polar aprotic solvents, and polar solvents can all be used as dispersion medium. The conductive films formed all show excellent adhesion (grade 5B of ASTM specification D2259). The resistivity (volume resistivity) of the conductive films is in the range of 3.0×10 ^-5 Ω. cm to 4.0×10 ^-5 Ω. cm and there is no great difference. This is because the dispersion medium evaporates in the drying step of drying the liquid film of the dispersion medium to form a particle film and in the firing step of firing the particle film to form a conductive film. In addition, not only the first embodiment of the present invention, but also the second embodiment has the same drying step and firing step.

In Examples 1 to 39, the firing temperature is 150°C. In order to investigate the effect of the firing temperature, the same experiment was performed with the firing temperature changed as an example of the first embodiment.

[Example 40]

The firing temperature is 200°C, which is higher than 150°C in Example 1. Other experimental conditions (dispersant, concentration of copper nanoparticles, dispersant and its concentration, epoxy resin and its concentration, hardener and its concentration, etc.) are the same as in Example 1.

After firing, a conductive film was formed. The adhesiveness of the conductive film was the same as that of Example 1, which was Grade 5B. The resistivity of the conductive film was lower than that of Example 1, which was 2.0×10 ^-5 Ω·cm.

[Example 41]

The firing temperature is 250°C, which is higher than that of Example 40. Other experimental conditions (dispersant, concentration of copper nanoparticles, dispersant and its concentration, epoxy resin and its concentration, hardener and its concentration, etc.) are the same as those of Example 40.

After firing, a conductive film was formed. The adhesiveness of the conductive film was the same level 5B as that of Example 1. The resistivity of the conductive film was 1.2×10 ^-5 Ω·cm, which was lower than that of Example 40.

Comparison of Example 1 (firing temperature 150°C, resistivity 2.0×10 ^-4 Ω·cm), Example 40 (firing temperature 200°C, resistivity 2.0×10 ^-5 Ω·cm), and Example 41 (firing temperature 250°C, resistivity 1.2×10 ^-5 Ω·cm) shows that the higher the firing temperature, the lower the resistivity of the conductive film formed. However, a high firing temperature may have a thermal effect on the target object (electronic device). The firing temperature is preferably set in consideration of the heat resistance of the target object for forming the conductive film.

(Comparative example 4)

The heating temperature in the firing step is set to 100°C, which is lower than the firing temperature of 150°C in Example 1. 100°C is the same as the boiling point of water. Other experimental conditions (dispersant, concentration of copper nanoparticles, dispersant and its concentration, epoxy resin and its concentration, hardener and its concentration, etc.) are the same as in Example 1.

After firing, a conductive film is formed. In the tape peeling test of the conductive film, the peeled pieces are grade 0B of ASTM specification D2259. Grade 0B means that the peeled pieces exceed 65%. The resistivity of the conductive film is 2.5×10 ^-3 Ω·cm, which is about one digit higher than that of the embodiment. That is, when the heating temperature is lowered to a level that can hardly be called the firing temperature, even if a conductive film is formed, the adhesion of the conductive film cannot be obtained and the resistivity of the conductive film is high.

In addition, the present invention is not limited to the structure of the above-mentioned embodiment, and various modifications are possible without changing the scope of the invention. For example, in the conductive film forming method, the target 2 may not be placed on the working surface 3, but the bottom and wires of the target 2 may be held by tools, etc. In addition, the target 2 is not limited to electronic devices. In addition, the conductive film 1 may be formed on the bottom surface of the target 2.

1: Conductive film

2: Target object

3: Working surface

4: Liquid film

5: Particle film

21: Top

22:Side

23: Bottom

Claims (6)

A conductive film forming method is to form a conductive film on the surface of a target object using a conductive composition that exhibits conductivity after firing, wherein the conductive composition contains copper nanoparticles, a liquid dispersion medium, a dispersant for dispersing the copper nanoparticles in the dispersion medium, and a thermosetting organic matrix, wherein the dispersant is a polymer compound containing nitrogen atoms or phosphorus atoms, and the organic matrix is a liquid epoxy resin and a hardener for curing the epoxy resin. The curing agent is an alkaline nitrogen-containing compound, the concentration of the epoxy resin is greater than 1.0 mass % and less than 4.7 mass % relative to the entire conductive composition, and the conductive film forming method has the following steps: forming a liquid film composed of the conductive composition on the surface of the target object; drying the liquid film to form a particle film; and firing the particle film in a formic acid environment to form a conductive film and harden the epoxy resin. A method for forming a conductive film, wherein a conductive composition that exhibits conductivity after firing is used to form a conductive film on the surface of a target object, wherein the conductive composition contains copper nanoparticles, a liquid dispersion medium, a dispersant for dispersing the copper nanoparticles in the dispersion medium, and a thermosetting organic matrix, wherein the dispersant is a polymer compound containing nitrogen atoms or phosphorus atoms, and the organic matrix is composed of a liquid epoxy resin and a hardener for hardening the epoxy resin, wherein the hardener is an alkaline nitrogen-containing compound, and the concentration of the epoxy resin is 100% relative to the The conductive composition is 1.0 mass % or more and 4.7 mass % or less. The conductive film forming method has the following steps in sequence: forming a liquid film composed of the conductive composition on the surface of the target object; drying the liquid film to form a particle film; immersing the target object formed with the particle film in a formic acid aqueous solution; taking out the target object formed with the particle film from the formic acid aqueous solution and removing the liquid on the particle film; and firing the particle film in a passive environment to form a conductive film and harden the epoxy resin. A conductive film forming method as claimed in claim 1 or 2, wherein the concentration of the copper nanoparticles is greater than 35.9 mass % and less than 39.1 mass % relative to the entire conductive composition. A conductive film forming method as claimed in claim 1 or 2, wherein the dispersant is a branched polyester or phosphate polyester having an amine. A conductive film forming method as claimed in claim 1 or 2, wherein the hardener is an amine. As in claim 5, the conductive film forming method, wherein the hardener is selected from the group consisting of imidazole derivatives, modified amines and phenolic aromatic amines.

Images