WO2014021037A1

WO2014021037A1 - Electroconductive film

Info

Publication number: WO2014021037A1
Application number: PCT/JP2013/067862
Authority: WO
Inventors: 卓藤本; 昌宏三輪; 康成脇森; 林　富雄; 晃祐織田; 隆障子口; 宏幸森中
Original assignee: 三井金属鉱業株式会社
Priority date: 2012-08-02
Filing date: 2013-06-28
Publication date: 2014-02-06
Also published as: TW201413749A; TWI590261B; JP5503813B1; JPWO2014021037A1

Abstract

The present invention pertains to an electroconductive film in which silver-coated copper powder is used, and provides a novel electroconductive film in which the desired electroconductive properties can be obtained even without adding silver powder. An electroconductive film in which an electroconductive film containing dendritic silver-coated copper powder particles is provided on a substrate film, wherein silver-coated copper powder particles in which at least a part of the surface of copper powder particles is covered by silver are used as the dendritic silver-coated copper powder particles. When the silver-coated copper powder particles are observed using a scanning electron microscope (SEM), the particles have a dendritic shape provided with a single main axis and a plurality of branches branching off from the main axis in perpendicular or diagonal directions, and resulting from two- or three-dimensional growth. The thickness (a) along the main axis is 0.3 to 6.0 μm. The length (b) of the longest of the branches extending from the main axis is 0.3 to 10.0 μm.

Description

Conductive film

The present invention relates to a conductive film provided with a conductive film.

Various electromagnetic shielding materials have been developed in response to the requirement that electromagnetic waves generated from a display leak outside and prevent adverse effects on the human body.
The electromagnetic shielding material is classified into an electromagnetic shielding material made of a transparent conductive film and an electromagnetic shielding material made of a conductive metal mesh. Among these, the electromagnetic wave shielding material made of a conductive film is said to be inferior in electromagnetic wave shielding performance due to its high surface resistivity while being excellent in transparency compared to the electromagnetic wave shielding material made of metal mesh. Therefore, regarding the electromagnetic wave shielding material using a conductive film, increasing the conductivity of the conductive film has been one of the important issues.

As an electromagnetic shielding material using a conductive film, for example, a conductive paste in which metal powder as a conductive material is dispersed in a binder resin is applied to a base film to form a conductive layer, and a protective layer is further formed thereon. What is formed is known.
At this time, silver powder has been conventionally used as a metal powder as a conductive material. However, silver powder is expensive, so silver-coated copper powder obtained by plating silver on the surface of copper powder particles by electroless plating or the like. (Also referred to as “silver coated copper powder”) is beginning to be used.

For example, Patent Document 1 discloses that a scaly silver powder having an average particle size of 2.0 to 5.0 μm and a dendritic tree having an average particle size of 10 to 19 μm are used in order to obtain a conductive paste composition that satisfies the bending characteristics required by a flexible substrate. It is disclosed to use a mixed powder with a silver-plated copper powder.

Patent Document 2 discloses that in an electromagnetic wave shielding film in which a protective layer is laminated on a conductive layer made of (A) metal powder and (B) a binder resin, the conductive layer (a) has an average thickness of 50 to 300 nm. And a conductive paste containing flaky metal powder having an average particle diameter of 3 to 10 μm and (b) acicular or dendritic metal powder (particularly silver-coated copper powder) having an average particle diameter of 3 to 10 μm. Are disclosed.

JP 2009-230952 A JP 2011-187895 A

Conventionally, in a conductive film such as an electromagnetic wave shielding film, even if silver-coated copper powder is used as a conductive material, as described in Patent Documents 1 and 2, if a predetermined amount or more of silver powder is not mixed, desired conductive characteristics are obtained. Therefore, the cost was increased by the amount of silver powder mixed.

Therefore, the present invention relates to a conductive film provided with a conductive film using silver-coated copper powder as a conductive material, and provides a new conductive film that can obtain desired conductive characteristics without blending silver powder. To do.

The present invention is a conductive film comprising a conductive film containing dendritic silver-coated copper powder particles on a base film, wherein the dendritic silver-coated copper powder particles are at least part of the surface of the copper powder particles Is a silver-coated copper powder particle coated with silver, and when the silver-coated copper powder particle is observed using a scanning electron microscope (SEM), it has one main axis and is orthogonal to the main axis. A plurality of branches branch in a direction or oblique direction to form a dendritic shape that grows two-dimensionally or three-dimensionally, and the thickness a of the main axis is 0.3 μm to 6.0 μm, and from the main axis A conductive film characterized by dendritic silver-coated copper powder particles having a longest branch length b of 0.3 μm to 10.0 μm among the extended branches is proposed.

The silver-coated copper powder used in the present invention is a silver-coated copper powder particle having a dendritic shape in which the branches branched from the main axis are significantly grown as compared with the conventional silver-coated copper powder. As compared with the above, the particles are further overlapped with each other, the number of contacts between the particles is further increased, and a further excellent electrical conductivity can be obtained. Therefore, sufficient conductive properties can be obtained without adding silver powder, and sufficient conductive properties can be obtained even if the amount of silver-coated copper powder particles is small. Therefore, not only an inexpensive and excellent conductive film can be obtained, but also the transparency of the film can be further increased, and therefore, for example, positioning when the films are bonded can be performed more easily.

It is a model figure of the silver covering copper powder particle which exhibits a dendrite shape. It is a photograph at the time of observing the electroconductive film which concerns on an example of this invention by the magnification of 2,000 times using the optical microscope. It is a photograph at the time of observing the electroconductive film which concerns on an example of this invention by the magnification of 3,000 times using the optical microscope.

Hereinafter, embodiments of the present invention will be described in detail. However, the scope of the present invention is not limited to the following embodiments.

<This conductive film>
The conductive film (referred to as “the present conductive film”) according to the present embodiment may be a film provided with a conductive film containing dendritic silver-coated copper powder particles on a base film.

<Base film>
As the substrate film, a transparent support film is preferably used. For example, a plastic film, a plastic plate, a glass plate, or the like can be used.
Examples of the raw material for the plastic film and plastic plate include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate; polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene, EVA; polyvinyl chloride, Vinyl resins such as polyvinylidene chloride; polyether ether ketone (PEEK), polysulfone (PSF), polyether sulfone (PES), polycarbonate (PC), polyamide, polyimide, acrylic resin, triacetyl cellulose (TAC) Etc. can be used.

<Conductive film>
The conductive film only needs to be a layer containing dendritic silver-coated copper powder particles and a binder resin, and is a single layer consisting of only the layer containing dendritic silver-coated copper powder particles (so-called “isotropic conductive film”). Or a multilayer (so-called “anisotropic conductive film”) in which another layer is stacked on the layer.

(Dendrite-like silver-coated copper powder particles)
The dendrite-like silver-coated copper powder particles are silver-coated copper powder particles obtained by coating at least part of the surface of the copper powder particles as a core material with silver and exhibit a dendrite-like shape (“the present silver-coated copper Called "powder particles").
In the present silver-coated copper powder particles, it is sufficient that at least a part of the surface of the copper powder particles as the core material is coated with silver, and the entire surface of the copper powder particles may be coated with silver. In addition, a part of the surface of the copper powder particles may be exposed.

Here, “dendritic” means having a single main axis when observed with an optical microscope or an electron microscope (500 to 20,000 times), and a plurality of branches in an orthogonal direction or an oblique direction from the main axis. Means a particle which branches and exhibits a shape grown two-dimensionally or three-dimensionally. It does not include those in which wide leaves gather to form a pinecone shape or a shape in which a large number of needle-like portions do not have a main shaft and extend radially.

The present silver-coated copper powder particles contain, among the dendritic copper powder particles, particles exhibiting a dendritic shape having the following characteristics when observed with an optical microscope or an electron microscope (500 to 20,000 times). Is preferred (see FIG. 1).
-It is important that the thickness a of the main shaft is 0.3 μm to 6.0 μm, especially 0.4 μm or more and 4.5 μm or less, especially 0.5 μm or more or 4.0 μm or less. preferable. When the thickness a of the main shaft of the dendrites is less than 0.3 μm, the main shaft is not firm, so it easily breaks during paste kneading. .
The major axis L of the main shaft is preferably 0.1 μm to 100.0 μm, more preferably 0.5 μm or more and 50 μm or less, and particularly preferably 1 μm or more or 30 μm or less.

The longest branch length b (referred to as “branch length b”) among the branches extending from the main axis indicates the degree of dendrite growth, and is important to be 0.3 μm to 10.0 μm. In particular, 0.5 μm or more or 9.0 μm or less, and more preferably 0.7 μm or more or 8.0 μm or less. If the branch length b is less than 0.3 μm, it cannot be said that the dendrite has grown to an extent sufficient to obtain excellent conduction. On the other hand, when the branch length b exceeds 10.0 μm, the fluidity of the copper powder is lowered and the handling becomes difficult.
The number of branches with respect to the major axis L of the main axis (number of branches / major axis L) indicates the number of dendrite branches and is preferably 0.1 / μm to 5.0 / μm, especially 0 .3 / μm or more or 4.5 / μm or less, of which 0.5 / μm or more or 4.0 / μm or less, of which 0.8 / μm or more or 3.5 / μm In the following, it is more preferable that the number is 1.0 / μm or more or 3.0 / μm or less. If the number of branches / major axis L is 0.1 / μm or more, the number of branches in the film is sufficiently large and sufficient contact can be secured, while the number of branches / major axis L is 5.0 / μm or less. If it exists, it can prevent that the fluidity | liquidity of this copper powder becomes inferior because there are too many branches.

However, when most of the silver-coated copper powder particles contained in the conductive film are dendrite-like particles as described above when observed with an optical microscope or an electron microscope (500 to 20,000 times), particles of other shapes are used. Even if mixed, the same effect as that of the silver-coated copper powder particles composed only of the dendritic particles as described above can be obtained. Therefore, from this point of view, when the conductive film is observed with an optical microscope or an electron microscope (500 to 20,000 times), the above silver-coated copper powder particles are 60% by number or more of the total silver-coated copper powder particles. The non-dendritic silver-coated copper powder particles that are not recognized as dendritic may be included as long as they account for 80% by number or more, more preferably 90% by number or more.

As a method for producing the present silver-coated copper powder particles, the dendritic copper powder as a core material is dispersed in water, a chelating agent is added, and then a water-soluble silver salt is added to cause a substitution reaction to obtain copper powder particles. After the surface layer is replaced with silver, the obtained silver-coated copper powder is taken out of the solution, washed with a chelating agent, and dried. However, it is not limited to this manufacturing method.

Compared to the reduction plating coating method, the displacement plating coating method can not only uniformly coat the surface of the core material (copper powder particles) with silver, but also can suppress the aggregation of particles after coating. Therefore, it is preferable to employ the displacement plating coating method because it has a feature that it can be manufactured at a lower cost.

In the conventional displacement plating coating method, when silver-coated copper powder is taken out from the reaction solution, it is filtered and washed with water or the like. However, just washing with water will cause some of the copper ions to be adsorbed on the silver-coated copper powder, so copper ions will remain on the surface of the particles. As a result, a copper oxide film could be formed on the particle surface.
In contrast, by washing with a chelating agent, copper re-adsorption after the substitution reaction can be prevented, so that copper ions remaining on the particle surface can be suppressed. Conductivity can be improved by suppressing the formation of a copper film.
In the case of washing with a chelating agent, the chelating agent may remain, so that it is preferable to wash with pure water or the like.

Examples of the chelating agent include ethylenediaminetetraacetic acid salt (hereinafter referred to as “EDTA”), aminocarboxylic acid-based chelating agents such as diethylenetriaminepentaacetic acid and iminodiacetic acid, hydroxyethylethylenediaminetriacetic acid, dihydroxyethylethylenediaminediacetic acid), 1 , 3-propanediaminetetraacetic acid, one or two or more selected from propanediaminetetraacetic acid can be mentioned, and among these, EDTA is preferably used.

When adding the silver salt, the pH of the solution, that is, the pH of the solution during the substitution reaction is preferably adjusted to 3-7.
Silver salts soluble in water, that is, Ag ion sources include silver nitrate, silver perchlorate, silver acetate, silver oxalate, silver chlorate, silver hexafluorophosphate, and boron tetrafluoride. One or more selected from acid silver, silver hexafluoroarsenate, and silver sulfate can be mentioned.

The amount of silver salt added is preferably equal to or greater than the theoretical equivalent, for example, when copper is used as the core material, the amount of silver is 2 mol or more, particularly 2.1 mol or more with respect to 1 mol of copper. When the amount is less than 2 mol, the substitution is insufficient and a large amount of copper remains in the silver powder particles. However, it is not economical to add 2.5 mol or more.

The silver content in the silver powder particles can be adjusted by the amount of silver salt added, the reaction time, the reaction rate, the amount of chelating agent added, and the like.
After completion of the substitution reaction, the silver powder particles are preferably thoroughly washed and dried.

As the copper powder used as the core material, it is preferable to use a copper powder exhibiting a dendrite shape with sufficiently developed branches. If silver is coated by the above method, the shape of the copper powder particles used as the core material can be converted into the particle shape of the present silver-coated copper powder almost as it is.

The above-described copper powder having a dendritic shape with sufficiently developed branches can be produced by the following electrolytic method.

As a method for producing such a copper powder, for example, an anode and a cathode are immersed in a sulfuric acid electrolytic solution containing copper ions, a direct current is passed through the electrolyte, and copper is deposited on the cathode surface in a powder form. And a method of producing copper powder through a sieving step or the like, if necessary, by scraping and collecting by mechanical or electrical methods, washing, drying.

When copper powder is produced by the electrolytic method, the copper ions in the electrolyte solution are consumed as copper is deposited, so the copper ion concentration in the electrolyte solution near the electrode plate is reduced, and the electrolytic efficiency decreases as it is. End up. Therefore, normally, in order to increase the electrolysis efficiency, the electrolyte solution in the electrolytic cell is circulated so that the copper ion concentration of the electrolyte solution between the electrodes does not become thin.
However, it has been found that in order to develop the dendrite of each copper powder particle, in other words, to promote the growth of branches extending from the main axis, it is preferable that the copper ion concentration in the electrolyte solution near the electrode is low. Therefore, in the production of electrolytic copper powder, the size of the electrolytic cell, the number of electrodes, the distance between the electrodes, and the circulation amount of the electrolytic solution are adjusted, and the copper ion concentration of the electrolytic solution in the vicinity of the electrodes is adjusted to be low. It is preferable to adjust so that the copper ion concentration of the electrolyte solution between electrodes is always thinner than the copper ion concentration of the electrolyte solution at the bottom.

Here, one model case is introduced. When the electrolytic cell size is 2 m ³ to 10 m ³ , the number of electrodes is 10 to 40, and the distance between the electrodes is 5 cm to 50 cm, the copper ion concentration is 1 g / By adjusting the circulating amount of the electrolytic solution of L to 50 g / L to 10 to 100 L / min, dendrites can be developed, and electrolytic copper powder having a dendritic shape with sufficiently developed branches can be obtained.

In order to adjust the particle size of the dendritic copper powder particles, conditions may be set as appropriate based on common general technical knowledge within the range of the above conditions. For example, if it is intended to obtain dendritic copper powder particles having a large particle size, the copper concentration is preferably set to a relatively high concentration within the above preferred range, and the current density is relatively low within the above preferred range. The density is preferably set, and the electrolysis time is preferably set to a relatively long time within the above preferable range. If it is intended to obtain dendritic copper powder particles having a small particle size, it is preferable to set the respective conditions based on the opposite concept. As an example, the copper concentration may be 1 g / L to 20 g / L, the current density may be 50 A / m ² to 1000 A / m ² , and the electrolysis time may be 5 minutes to 12 hours.

The core material is preferably subjected to a treatment for removing the surface oxide (oxide film) before the substitution reaction, if necessary. For example, after the core material is put into water and stirred and mixed, a reducing agent such as hydrazine is added and stirred and mixed to react. At this time, it is preferable that the added reducing agent is sufficiently washed and removed from the core material.

(Binder resin)
As the binder resin, for example, epoxy resin, phenol resin, unsaturated polyester resin, polyurethane resin, acrylic resin, melamine resin, polyimide resin, polyamideimide resin, and the like can be used. However, it is not limited to these.

(Mixing amount)
The content of the silver-coated copper powder particles in the conductive film may be 2 to 85% by mass of the entire conductive film. The present silver-coated copper powder particles have a feature that electrical conductivity can be obtained even with a small amount. Thus, for example, in the case of a conductive film consisting only of a layer containing the silver-coated copper powder particles (so-called “isotropic conductive film”), the content of the silver-coated copper powder particles is about 30 to 50% by mass. In addition, electromagnetic wave shielding characteristics can be obtained. However, more preferable conductivity can be obtained if the content of the silver-coated copper powder particles is higher.
In addition, in the case of a conductive film (so-called “anisotropic conductive film”) composed of two layers of a layer containing the present silver-coated copper powder particles and another conductive layer, for example, a conductive layer containing silver, the number is remarkably small. For example, it may be about 2 to 5% by mass.

(Other ingredients)
The conductive film may contain components other than the binder resin and the present silver-coated copper powder particles.
For example, silver particles may be included. The shape of the silver particles is not particularly limited, and examples thereof include a spherical shape and a scale shape.
However, since this conductive film can obtain electrical continuity even if it does not contain silver particles, the conductive material contained in the conductive film (in this case, the total of dendritic silver-coated copper powder particles and silver particles) The present silver-coated copper powder particles preferably occupy 80% by number or more, particularly 90% by number or more.

(Thickness of conductive film)
The thickness of the conductive film is not particularly limited, and greatly varies depending on whether the conductive film is an anisotropic conductive film or an isotropic conductive film. In any case, the thickness is preferably in the range of 5 μm to 60 μm. If the thickness is 5 μm or more, desirable conductivity can be obtained, and if the thickness is 50 μm or less, the flexibility of the conductive film can be maintained, bending characteristics can be maintained, and cost can be reduced. .

(Method for forming conductive film)
The conductive film can be formed by applying a conductive paste to a base film.

For example, in order to produce a conductive paste, the present silver-coated copper powder is mixed with a binder and a solvent, and further, if necessary, a curing agent, a coupling agent, a corrosion inhibitor, etc., without breaking the shape of the present silver-coated copper powder. It is preferable to prepare an electrically conductive paste by kneading so as to be dispersed in the paste. Specifically, avoid the use of a stirrer that gives mechanical impact to the powder, for example, kneading without giving mechanical impact, such as using Awatori Netaro (trade name) or planetary mixer. It is preferable to prepare a conductive paste.

Examples of the binder include, but are not limited to, liquid epoxy resins, phenol resins, unsaturated polyester resins, and the like.
Examples of the solvent include terpineol, ethyl carbitol, carbitol acetate, butyl cellosolve and the like.
Examples of the curing agent include 2-ethyl 4-methylimidazole.
Examples of the corrosion inhibitor include benzothiazole and benzimidazole.
Additives such as thickeners and leveling agents can also be added. Furthermore, it is also possible to add inorganic fillers, such as carbon and a silica, as needed.

Examples of the method for applying the conductive paste include screen printing, intaglio printing, lithographic printing, and dispenser. Screen printing is most preferably used from the viewpoint of the fineness, film thickness, and productivity of the formed wiring.

(Other layers)
If necessary, it is optional to provide another layer between the base film and the conductive film or outside the conductive film.
For example, it is possible to provide a protective layer that exhibits an effect of preventing scratches and improving mechanical properties on the outside of the conductive film. Under the present circumstances, the film which comprises a protective layer can be formed, for example with an epoxy resin, a urethane resin, etc.
The surface hardness of the protective layer is preferably H to 4H in terms of pencil hardness. For this purpose, an acrylic hard coat layer can be laminated on the layer made of the epoxy resin or urethane resin as necessary.
If the surface hardness of the protective layer is less than H as the pencil hardness, the protective layer is likely to be damaged, whereas if it is greater than 4H, the flexibility is reduced and the sliding characteristics may be deteriorated.

<Characteristics and use of this conductive film>
The conductive film can obtain conductivity without using silver powder as a conductive material, and can obtain conductivity even when the content of dendritic silver-coated copper powder particles is small. Can do. Therefore, the transparency of the film can be increased. Moreover, it has excellent electromagnetic shielding characteristics.
Since this electroconductive film is provided with such a characteristic, it can be utilized as electroconductive films, such as an electromagnetic wave shield film, a bonding film which connects a circuit board and a circuit board, and an antistatic film, for example. Especially, it can utilize especially preferably as an electromagnetic wave shielding film.

Regarding the electromagnetic wave shielding film, even if it is an isotropic conductive film that forms a conductive film only from the layer containing the present silver-coated copper powder particles, the layer containing the present silver-coated copper powder particles and other conductive film layers, For example, any anisotropic conductive film that forms a conductive film from two layers such as a silver film layer can be formed.

As the electromagnetic wave shielding film, for example, a flexible substrate in which a conductive film is formed on a flexible substrate by placing the conductive film on a flexible substrate and performing a pressing process of heating while pressing at a pressure of 1 to 5 MPa. Can be formed. Also in this case, it is preferable to press the silver-coated copper powder without breaking the shape.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is greater than X” and “preferably greater than X” or “preferably greater than Y”. The meaning of “small” is also included.
In addition, when expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and expressed as “Y or less” (Y is an arbitrary number). In the case, unless otherwise specified, the meaning of “preferably smaller than Y” is included.

Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the following examples.

<Observation of particle shape>
Using the optical microscope (2,000 times), the films obtained in the examples and comparative examples were observed for the shape of 500 particles in an arbitrary 100 field of view, and the main axis thickness a (“main axis thickness”). A "), the length L of the main axis, the length b of the longest branch among the branches extending from the main axis (" branch length b "), and the number of branches with respect to the major axis of the main axis (" number of branches / major axis L ") ) And the average value is shown in Table 1.

<Transmissivity>
The transmissivity (TT%) of the film obtained by the Example and the comparative example was measured using the translucent meter ("NDH2000" made by Nippon Denshoku).

<Sheet resistance>
Measurements were made by the four probe method. Specifically, using a measurement device in which a voltmeter “34420A” also manufactured by Agilent Technologies, Inc., is connected to a semiconductor device analyzer “B1500A” manufactured by Agilent Technologies, at 100 mA, it is obtained in Examples and Comparative Examples. The sheet resistance of the electromagnetic shielding film was measured.

<Bending resistivity change value>
The films produced in Examples and Comparative Examples were folded 100 times, and the specific resistance before and after folding (Ω / □) was measured. Table 1 shows the relative value when the value of the specific resistance (Ω / □) after bending is set to 1.00 and the specific resistance (Ω / □) before bending is 1.00. Indicated by value.

<Example 1>
28.0 parts by mass of silver-coated copper powder, 34.3 parts by mass of an epoxy-based thermosetting resin as a binder, and 37.7 parts by mass of a MEK / PGM mixed solvent (mixing ratio 3/2) as a solvent, A conductive paste was prepared by kneading using a stirrer (“Awori Nertaro” manufactured by Shinky Co., Ltd., planetary mixer manufactured by Asada Tekko Co., Ltd.) so as to maintain the shape of the silver-coated copper powder particles.
This conductive paste is applied to the surface of a 25 μm-thick fluororesin film (“Aflex” manufactured by Asahi Glass) with an applicator so as to have a thickness of 30 μm, and a conductive film (electromagnetic wave shield) is formed. Film). At this time, the content rate of the silver covering copper powder in a electrically conductive film was 45 wt%.

What was manufactured as follows was used for the said silver covering copper powder.
In an electrolytic cell having a size of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), nine copper cathode plates and a copper anode plate (electrodes) each having a size (1.0 m × 1.0 m) are electrodes. Suspended so as to have a distance of 5 cm, and circulated a copper sulfate solution as an electrolytic solution at 30 L / min, immersed an anode and a cathode in this electrolytic solution, and conducted a direct current to conduct electrolysis. Powdered copper was deposited on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 10 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 100 g / L, and a current density of 80 A / m ² for electrolysis for 1 hour.
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was always kept lower than the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.
Then, the copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrated copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water, 1 L of an industrial gelatin (made by Nitta Gelatin Co., Ltd.) 10 g / L aqueous solution was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then under reduced pressure (1 × 10 ⁻³ Pa) at 80 ° C. for 6 hours to obtain electrolytic copper powder.
25 kg of the obtained electrolytic copper powder was put into 50 L of pure water kept at 50 ° C. and stirred well. Separately, 4.5 kg of silver nitrate was put into 5 L of pure water to prepare a silver nitrate solution. The silver nitrate solution was added all at once to the solution in which the copper powder was dissolved. In this state, stirring was performed for 2 hours to obtain a silver-coated copper powder slurry.
Next, the silver-coated copper powder slurry is filtered by vacuum filtration. After the filtration is completed, the slurry is washed with a solution obtained by dissolving 600 g of EDTA (ethylenediaminetetraacetic acid) in 6 L of pure water, followed by 3 L of pure water. Residual EDTA was washed with water. Then, it was made to dry at 120 degreeC for 3 hours, and dendritic silver covering copper powder (sample) was obtained. The silver coating amount was 10.8% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using an optical microscope, at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It has a dendritic shape that branches into a three-dimensional growth and has a main axis thickness a: 4.2 μm, a main shaft length L: 20.3 μm, a branch length b: 7.4 μm, and the number of branches / major axis L: The number was 1.6 / μm.
As shown in Table 1, the sheet resistance of this conductive film showed a good value.

<Example 2>
A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 18.7 parts by mass of the silver-coated copper powder and 43.6 parts by mass of the epoxy thermosetting resin as the binder were used. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 30 wt%.

An electrolytic copper powder was obtained in the same manner as in Example 1 except that the Cu concentration of the electrolytic solution was 5 g / L, the electrolysis time was 40 minutes, and the amount of circulating liquid was 20 L / min. Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.9% by mass of the total silver-coated copper powder.
When the obtained dendrite-like silver-coated copper powder (sample) was observed using an optical microscope, at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It has a dendrite-like shape that branches into a three-dimensional growth and has a main axis thickness a: 1.8 μm, a main shaft length L: 14.9 μm, a branch length b: 3.9 μm, and the number of branches / major axis L: The number was 1.5 / μm.

<Example 3>
A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 28.0 parts by mass of the silver-coated copper powder and 34.3 parts by mass of the epoxy thermosetting resin as the binder were used. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 45 wt%.

An electrolytic copper powder was obtained in the same manner as in Example 1 except that the Cu concentration of the electrolytic solution was 6 g / L, the circulating liquid amount was 20 L / min, the electrolysis time was 40 minutes, and the current density was 150 A / m ² . Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.8% by mass of the total silver-coated copper powder.
When the obtained dendrite-like silver-coated copper powder (sample) was observed using an optical microscope, at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It has a dendritic shape that is branched into three dimensions and grows three-dimensionally. Main shaft thickness a: 2.1 μm, main shaft length L: 14.6 μm, branch length b: 4.2 μm, number of branches / major axis L: It was 3.1 / μm.
As shown in Table 1, the sheet resistance of this conductive film showed a good value.

<Example 4>
A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 40.5 parts by mass of the silver-coated copper powder and 21.8 parts by mass of the epoxy thermosetting resin as a binder were used. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 65 wt%.

An electrolytic copper powder was obtained in the same manner as in Example 1 except that the Cu concentration of the electrolytic solution was 1 g / L, the circulating liquid amount was 10 L / min, and the electrolysis time was 40 minutes. Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.7% by mass of the entire silver-coated copper powder.
When the obtained dendrite-like silver-coated copper powder (sample) was observed using an optical microscope, at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It has a dendrite-like shape that is branched into three-dimensionally and has a main shaft thickness a: 0.8 μm, a main shaft length L: 5.0 μm, a branch length b: 1.8 μm, the number of branches / long diameter L: It was 3.4 / μm.
As shown in Table 1, the sheet resistance of this conductive film showed a good value.

<Example 5>
A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 31.2 parts by mass of the silver-coated copper powder and 31.2 parts by mass of the epoxy thermosetting resin as the binder. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 50 wt%.

An electrolytic copper powder was obtained in the same manner as in Example 1 except that the Cu concentration of the electrolytic solution was 4 g / L, the circulating liquid amount was 10 L / min, the electrolysis time was 10 minutes, and the current density was 150 A / m ² .
Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.8% by mass of the total silver-coated copper powder.
When the obtained dendrite-like silver-coated copper powder (sample) was observed using an optical microscope, at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It has a dendrite-like shape branching into three dimensions and growing in a three-dimensional manner. Main axis thickness a: 1.4 μm, main axis length L: 6.0 μm, branch length b: 5.2 μm, number of branches / major axis L: The number was 2.5 / μm.
As shown in Table 1, the sheet resistance of this conductive film showed a good value.

<Example 6>
A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 28.0 parts by mass of the silver-coated copper powder and 34.3 parts by mass of the epoxy thermosetting resin as the binder were used. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 45 wt%.

Electrolysis was performed in the same manner as in Example 1 except that the Cu concentration of the electrolytic solution was 1 g / L, the circulating fluid amount was 40 L / min, the electrolysis time was 5 minutes, the current density was 150 A / m ² , and the circulating fluid amount was 10 L / min. Copper powder was obtained.
Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.5% by mass of the entire silver-coated copper powder.
When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It has a dendritic shape in which a plurality of branches obliquely branch and grow three-dimensionally. The main axis thickness a is 0.5 μm, the main axis length L is 3.1 μm, the branch length b is 2.9 μm, and the branches Number / major axis L: 3.0 / μm.
As shown in Table 1, the sheet resistance of this conductive film showed a good value.

<Comparative Example 1>
A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 40.5 parts by mass of the silver-coated copper powder and 21.8 parts by mass of the epoxy thermosetting resin as a binder were used. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 65 wt%.

In an electrolytic cell having a size of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), nine copper cathode plates and a copper anode plate (electrodes) each having a size (1.0 m × 1.0 m) are electrodes. Suspend so that the distance is 5 cm, circulate a copper sulfate solution as an electrolytic solution at 2 L / min, immerse the anode and the cathode in this electrolytic solution, conduct a direct current through this to perform electrolysis, Powdered copper was deposited on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 100 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 100 g / L, a circulating liquid amount of 2 L / min, and a current density of 80 A / m ² for electrolysis for 60 minutes. Carried out.
During electrolysis, the copper ion concentration in the electrolyte solution between the electrodes was always higher than the copper ion concentration in the electrolyte solution at the bottom of the electrolytic cell.
The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water, 1 L of an industrial gelatin (made by Nitta Gelatin) 10 g / L aqueous solution 1 L was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then washed at 80 ° C. in an air atmosphere. It was dried for 6 hours to obtain electrolytic copper powder.
Then, silver was coated in the same manner as in Example 1 to obtain a silver-coated copper powder (sample). The silver coating amount was 10.7% by mass of the entire silver-coated copper powder.

When the obtained silver-coated copper powder (sample) was observed using an optical microscope, the particle shape of the obtained electrolytic copper powder was pine cone-shaped, and the measurement of the spindle thickness, branch length, number of branches / long diameter L was I could not do it.
As shown in Table 1, the sheet resistance of this conductive film could not be measured due to overrange.

<Comparative Example 2>
40.5 parts by mass of silver-coated copper powder obtained by coating 10% by mass of silver on a copper powder particle (D50: 5 μm) having a spherical particle shape, and 21.8 parts by mass of an epoxy-based thermosetting resin as a binder A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 65 wt%.
As shown in Table 1, the sheet resistance of this conductive film could not be measured due to overrange.

<Comparative Example 3>
As a binder, 40.5 parts by mass of silver-coated copper powder obtained by coating 10% by mass of silver on a copper powder particle (average particle thickness: 1 μm, maximum particle diameter average: 5 μm) having a coin shape as a particle shape A conductive film (electromagnetic wave shielding film) was produced in the same manner as in Example 1 except that 21.8 parts by mass of the epoxy-based thermosetting resin was used. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 65 wt%.
As shown in Table 1, the sheet resistance of this conductive film could not be measured due to overrange.

<Comparative example 4>
40.5 parts by mass of silver-coated copper powder which is a commercially available silver-coated copper powder and has a dendritic shape with an underdeveloped particle shape, and 21.8 parts by mass of an epoxy-based thermosetting resin as a binder A conductive film (electromagnetic wave shield film) was produced in the same manner as Example 1 except for the above. At this time, the content rate of the silver covering copper powder in a electrically conductive film was 65 wt%.
As shown in Table 1, the sheet resistance of this conductive film showed a slightly high value.

(Discussion)
Considering the above examples and the results of the tests conducted so far, the conductive film provided with the conductive film using silver-coated copper powder as the conductive material was remarkably grown as a dendrite as in Example 1-6. If the conductive material containing the silver-coated copper powder particles is used, the required conductivity can be obtained without blending the silver powder as compared with the conventional silver-coated copper powder, and the amount of the silver-coated copper powder can be reduced. It has been found that the necessary conductivity can be obtained even with a small amount. This is because when silver-coated copper powder particles having dendritic shapes with significantly grown branches are used, the overlapping of the particles becomes denser and the number of contact points between the particles becomes larger, so even with a small amount, more It can be considered that more excellent electrical conductivity can be obtained.
And even if it reduces the quantity of silver covering copper powder, even if it is about 30 wt% (refer Example 2), as a result of obtaining the required electroconductivity, it can also improve the transparency of a film. I understood.

Claims

A conductive film comprising a conductive film containing dendritic silver-coated copper powder particles on a base film,
The dendrite-like silver-coated copper powder particles are silver-coated copper powder particles in which at least a part of the surface of the copper powder particles is coated with silver, and silver-coated copper powder particles using a scanning electron microscope (SEM). Is observed, it has a single main axis, a plurality of branches branch in an orthogonal direction or oblique direction from the main axis, exhibiting a dendritic shape that grows two-dimensionally or three-dimensionally, and the main axis Dendritic silver-coated copper powder particles having a thickness a of 0.3 μm to 6.0 μm and a longest branch length b of 0.3 μm to 10.0 μm among the branches extending from the main axis A conductive film characterized by that.
The dendrite-like silver-coated copper powder particles have a branching number (number of branches / major axis L) of 0.1 / μm to 4.0 / μm with respect to the major axis L of the main axis. Conductive film.