JP4090779B2 - Conductive composition, method for forming conductive film, conductive film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive composition used as a conductive paste, a conductive paint, a conductive adhesive, and the like, and a conductive film formed from the conductive composition and a method for forming the same. The conductivity is sufficiently increased.
[0002]
[Prior art]
Conventional conductive pastes include flaky silver particles, binders made of thermoplastic resins such as acrylic resins and vinyl acetate resins, thermosetting resins such as epoxy resins and polyester resins, organic solvents, curing agents, and catalysts. A silver paste obtained by adding and mixing is representative.
[0003]
This silver paste is widely used as a conductive adhesive, a conductive paint, and the like for various electronic devices, electronic components, electronic circuits, and the like. A flexible circuit board in which an electric circuit is formed by printing this silver paste on a plastic film such as a polyethylene terephthalate film by screen printing or the like is also used as a printed circuit board for keyboards and various switches.
[0004]
This silver paste is used by applying it to an object by various application means and drying at room temperature or heating to about 150 ° C. to form a conductive film.
The volume resistivity of the conductive film thus obtained is in the range of 10 ⁻⁴ to 10 ⁻⁵ Ω · cm depending on the film forming conditions, and the volume resistivity of metallic silver is 1.6. Compared to × 10 ⁻⁶ Ω · cm, the value is 10 to 100 times larger than the conductivity of metallic silver.
[0005]
The reason why the conductive film made of such a conventional silver paste has low conductivity is that only a part of the silver particles are in physical contact within the conductive film obtained from the silver paste, and the contact point is This is because there are few, there is contact resistance at the contact point, a binder remains between some silver particles, and this binder inhibits direct contact of the silver particles.
[0006]
In order to improve the low conductivity of such silver paste, the silver paste is applied to an object, heated to about 800 ° C., the binder is incinerated and removed, and the silver particles are melted. There is a method of forming a metal silver film that is uniformly and continuously fused. The volume resistivity of the conductive film thus obtained is about 10 ⁻⁶ Ω · cm, and has a conductivity close to that of metallic silver.
[0007]
However, this has a drawback that the object is limited to heat-resistant materials such as glass, ceramics, and enamel that can withstand high-temperature heating.
[0008]
Moreover, in the above-mentioned flexible circuit board, it is required to make the line width of the electric circuit formed thereon as thin as possible, but in the conventional silver paste, the silver particles have a particle size of 1 to 100 μm. In principle, it is impossible to print a circuit having a line width less than the particle size of the flaky silver particles.
[0009]
Moreover, despite the fact that the line width of the electric circuit is reduced, it is simultaneously required to have sufficient conductivity. To meet this requirement, the thickness of the electric circuit needs to be considerably increased. However, when the thickness of the electric circuit is increased, film formation becomes difficult and the flexibility of the circuit itself is greatly reduced.
[0010]
[Problems to be solved by the invention]
Therefore, the problem in the present invention is that a conductive film having a low volume resistivity and high conductivity comparable to metallic silver can be obtained and an electric circuit such as a flexible circuit board is formed without depending on the high temperature film forming conditions. In some cases, the line width of the electric circuit can be sufficiently narrowed, and a conductive composition that does not need to be thickened, a conductive film formed from the conductive composition, and a method for forming the same are obtained.
[0011]
[Means for Solving the Problems]
To solve this problem,
Such invention in claim 1, silver oxide, silver carbonate, silver acetate, and the particulate silver compound is one or more of acetylacetone silver complex, seen containing a dispersion medium, a dispersing agent, said dispersing agent is hydroxy It is a conductive composition of propylcellulose .
[0012]
The invention according to claim 2, the average particle diameter of the particulate silver compound is a conductive composition of claim 1 Symbol placement is 0.01 to 1 [mu] m.
The invention according to claim 3 is a method for forming a conductive film, in which the conductive composition according to claim 1 or 2 is applied and heated.
The invention according to claim 4 is a conductive film obtained by the method for forming a conductive film according to claim 3 , wherein silver particles are fused to each other.
[0013]
[Action]
The particulate silver compound is easily reduced to metallic silver particles simply by heating, and the metallic silver particles deposited by the reaction heat at the time of this reduction reaction melt and fuse together to form a highly conductive metallic silver coating. Form. For this reason, the conductive film obtained exhibits conductivity comparable to metallic silver.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments.
The particulate silver compound used in the conductive composition of the present invention is a solid particulate compound having the property of being reduced by simple heating to become metallic silver.
[0015]
Specific examples of the particulate silver compound include first silver oxide, second silver oxide, silver carbonate, silver acetate, and acetylacetone silver complex. These may be used in combination of two or more. As this particulate silver compound, those produced industrially can be used, and those obtained by reaction from an aqueous solution described later may be used.
[0016]
The average particle size of the particulate silver compound is in the range of 0.01 to 1 μm, preferably 0.01 to 0.5 μm, and can be appropriately selected according to the reduction reaction conditions; heating temperature and the like. In particular, it is preferable to use a particulate silver compound having an average particle size of 0.5 μm or less because the speed of the reduction reaction is increased. In addition, those having an average particle size of 0.5 μm or less are those produced by the reaction of a silver compound and other compounds, for example, an aqueous silver nitrate solution is reacted dropwise with an aqueous alkali solution such as sodium hydroxide while stirring to produce silver oxide. Can be produced by a method of obtaining In this case, it is desirable to add a dispersion stabilizer to the solution to prevent aggregation of the precipitated particulate silver compound.
[0017]
Further, a dispersion medium is used to disperse the particulate silver compound and obtain a liquid conductive composition. As the dispersion medium, water, alcohols such as ethanol, ethanol and propanol, and organic solvents such as isophorone, terpineol, triethylene glycol monobutyl ether and butyl cellosolve acetate are used.
[0018]
The selection of the type of dispersion medium and the amount used vary depending on the particulate silver compound and the film forming conditions, for example, screen printing, the mesh roughness of the printing plate, the fineness of the printing pattern, etc. Adjusted.
[0019]
Moreover, it is preferable to add a dispersing agent to disperse the particulate silver compound having an average particle diameter of 1 μm or less well to prevent secondary aggregation of the particulate silver compound. Hydroxypropyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, etc. are used for this dispersing agent, and the usage-amount is 0-300 weight part with respect to 100 weight part of particulate silver compounds.
[0020]
The conductive composition of the present invention is obtained by dispersing the above-mentioned particulate silver compound in a dispersion medium. Moreover, the dispersing agent may be added as needed. The particulate silver compound used here is preferably one having an average particle size of 1 μm or less and a small particle size because the reduction reaction rate is increased.
[0021]
Moreover, although the viscosity of this electroconductive composition changes with film forming conditions, about 30-300 poise is preferable, for example in the case of screen printing.
In addition, the conductive composition may be used by simply heating it after applying it to an object by an appropriate means. The heating temperature is 180 to 200 ° C., and the heating time is about 10 seconds to 120 minutes. Naturally, the surface of the object is kept clean.
[0022]
In the conductive film of the present invention thus obtained, the particulate silver compound is reduced, and the reduced metal silver particles are fused together to form a continuous thin film of metal silver. For this reason, the volume resistivity of the conductive film of the present invention shows a value ranging from 3 to 8 × 10 ⁻⁶ Ω · cm, which is in the same order as the volume resistivity of metallic silver.
[0023]
Moreover, since the average particle diameter of the particulate silver compound is 0.01 to 1 μm, the line width of the electric circuit formed by printing the conductive composition on the base material can be 1 μm or less, and the circuit Since its own conductivity is extremely high, there is no need to increase the thickness of the circuit. For this reason, it is easy to form a circuit, and the flexibility of the circuit itself is high.
[0024]
Furthermore, since the heating temperature for forming the conductive film is sufficient at 180 to 200 ° C., it can be applied to objects such as plastic films with low heat resistance, and can form a highly conductive film and target. There will be no thermal degradation of the product.
[0025]
Furthermore, since the volume resistivity of the obtained conductive film is very low, there is no problem even if the film thickness is very thin. The film thickness can be reduced by an amount corresponding to the decrease in volume resistivity with respect to the conventional conductive paste. For example, when a silver paste of 5 × 10 ⁻⁵ Ω · cm is used and the specification requires a circuit with a thickness of 50 μm, the present invention realizes a volume resistivity of 3 × 10 ⁻⁶ Ω · cm. Thus, the thickness can be 3 μm.
[0026]
In addition, since the surface of the conductive film obtained on the substrate side exhibits a mirror surface that is glossy of metallic silver, the back surface of a transparent substrate such as glass or plastic film or the substrate side of the conductive film peeled off from the substrate The surface can be used as a mirror having high reflectivity for home use, industrial use, and the like.
[0027]
Specific examples are shown below.
An aqueous solution in which 0.17 g of silver nitrate is dissolved in 50 ml of ion-exchanged water and 0.05 to 0.5 g of hydroxypropylcellulose (dispersing agent) is dissolved in this solution is prepared. .9-5 ml was dropped and stirring was continued for 10-30 minutes to obtain a silver oxide suspension.
[0028]
Subsequently, the silver oxide was washed 2-5 times with methanol to remove excess ions. Subsequently, ethanol (dispersion medium) was added thereto to produce a paste-like conductive composition of the present invention. The average particle diameter of silver oxide constituting this conductive composition was 200 to 500 nm.
[0029]
A pattern having a thickness of 5 to 10 μm was formed by screen printing on a polyimide film having a thickness of 0.1 mm from this conductive composition, and then this was heated in an oven at 180 ° C. for 30 minutes to 3 hours.
[0030]
The volume resistivity of the obtained pattern was 3-6 × 10 ⁻⁶ Ω · cm, and when the surface was observed with a scanning electron microscope, the silver particles reduced and precipitated from the silver oxide were fusion bonded. .
[0031]
For comparison, a pattern was formed in the same manner using silver paste (manufactured by Asahi Chemical Research Laboratories). The volume resistivity was 3 × 10 ⁻⁵ Ω · cm, and the surface was observed with a scanning electron microscope. As a result, the silver flakes were simply in contact with each other.
[0032]
【The invention's effect】
As described above, according to the conductive composition of the present invention, a highly conductive film can be obtained. Further, since the conductive film is formed by heating at a relatively low temperature, a plastic having low heat resistance or the like can be used as the base material. Furthermore, when an electric circuit is formed with this conductive composition, the line width of the electric circuit can be sufficiently narrowed, and it is not necessary to increase the thickness.

Claims (4)

Silver oxide, silver carbonate, silver acetate, and the particulate silver compound is one or more of acetylacetone silver complex, and a dispersion medium, seen containing a dispersing agent, and characterized in that the dispersing agent is hydroxypropyl cellulose conductive composition. The average particle diameter of the particulate silver compound, according to claim 1 Symbol placement of the electrically conductive composition characterized in that it is a 0.01 to 1 [mu] m. A method for forming a conductive film, comprising applying the conductive composition according to claim 1 or 2 and heating. Obtained by forming method according to claim 3, wherein the conductive coating, conductive coating, characterized in that the silver particles are fused together.