JP2003308729A - Conductive composition, conductive film and its formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive composition, a conductive film and its formation method having little restriction of a base material, and capable of enhancing conductivity and strength of the film. <P>SOLUTION: This conductive composition has a decomposition temperature of 200°C or below, and contains a silver compound having a melting point in a range below the decomposition temperature. In this case, a 10C or more tertiary fatty acid silver compound can be used for the silver compound. In this formation method of the conductive film, the conductive composition is applied to the surface of a base material to form a coating and the coating is heat-treated at 100-200°C to thermally decompose it. The conductive film is composed by heat-treating the conductive composition at 100-200°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive composition used as a conductive paste or the like. Moreover,
The present invention relates to a conductive coating film formed using the conductive composition and a method for forming the conductive coating film.

[0002]

2. Description of the Related Art Conductive compositions are widely used industrially in the production of electronic materials. Examples of the conductive composition include a conductive paste and the like. Further, as the conductive paste, for example, flake-shaped silver particles as a metal filler, an acrylic resin, a thermoplastic resin such as a vinyl acetate resin, an epoxy. Examples thereof include a silver paste obtained by adding a binder made of a thermosetting resin such as a resin or a polyester resin, an organic solvent, a curing agent, a catalyst, and the like and mixing them. This silver paste is used as a conductive adhesive and a conductive paint in various electronic devices, electronic parts, electronic circuits, and the like. A flexible circuit board in which an electric circuit is formed by printing a silver paste on a plastic film such as a polyethylene terephthalate film by screen printing is used for a printed circuit board such as a keyboard and various switches. This silver paste is applied on a base material by each application means, dried at room temperature or heat-treated at a temperature of room temperature to 200 ° C. to form a conductive film. The volume resistivity of this conductive film is usually in the range of 10 ⁻⁴ to 10 ⁻⁵ Ω · cm, although it depends on the film forming conditions. This value is 1 of the volume resistivity of metallic silver of 1.6 × 10 ⁻⁶ Ω · cm.
The value was 0 to 100 times higher, and the conductivity was significantly lower than that of metallic silver. Thus, the conductivity of the conductive coating formed from the conventional silver paste is low, the silver particles in the conductive coating are only partially in physical contact with each other, the number of contact points is small, Alternatively, the main reason is that the binder remains between some of the silver particles, and the remaining binder hinders direct contact of the silver particles.

[0003]

Therefore, for the purpose of improving the conductivity, the silver paste applied to the base material is heated to 500 ° C. or higher to incinerate the binder and remove it, and at the same time fuse the silver particles. A method for forming a uniform and continuous metallic silver coating has been proposed. The volume resistivity of the conductive coating film thus obtained is 10 ⁻⁶ Ω · cm, and the conductivity is almost equal to that of metallic silver. However, there has been a problem that the base material is limited to heat resistant materials such as glass, ceramics and enamel which can withstand high temperature heating.

A conductive composition containing, in addition to a metal filler, a fatty acid metal salt compound (metal organic resinate) which is a metal component is disclosed in, for example, JP-A-2-227909.
JP-A No. 7-176448 and the like. In these inventions, the fatty acid metal salt compound is said to decompose during firing to deposit metal atoms and aid sintering between the metal fillers. Further, for example, Japanese Patent Laid-Open No. 2-2
No. 08373, JP-A-6-139816 and the like describe forming a conductive coating from a conductive composition containing a fatty acid metal salt as a main component without containing a conductive filler such as a metal filler. There is. In this case, since it is not necessary to fuse the conductive filler, the metal coating can be formed at a relatively low temperature. Further, a conductive composition containing no binder is described in JP-A-5-89716.
However, in order to thermally decompose the fatty acid silver compound proposed in the above invention, it is necessary to heat at 200 ° C. or higher, and in order to form a conductive silver film, 300 to 500 is required.
Often heated to ° C. Therefore, the limitation of usable substrates has not been solved.

Further, the fatty acid silver compound is usually dissolved in a solvent, but when heated, the solvent may be exhausted before decomposition. Since the fatty acid silver compound proposed in the above invention does not become liquid until it is decomposed, in such a case, the fatty acid silver compound becomes a non-uniform particle mass while the dispersion state of the fatty acid silver compound is low. When further heated, the fatty acid silver compound is thermally decomposed as it is, so that the silver produced by the decomposition also becomes a granular mass, and the denseness and uniformity of the formed film are low. The coating film with low density and uniformity has a problem that the conductivity and the strength of the coating film are low because there are few places where silver particles are fused to each other. An object of the present invention is to provide a conductive composition, a conductive coating, and a method for forming the same, which have a small restriction on the base material and can enhance the conductivity and the strength of the coating.

[0006]

The conductive composition of the present invention is characterized by having a decomposition temperature of 200 ° C. or lower and containing a silver compound having a melting point in a temperature range lower than the decomposition temperature. If it has a melting point in the temperature region lower than the decomposition temperature, when heated, it melts and becomes a liquid before it is thermally decomposed, so that the formation of particulate lumps is prevented. Therefore, since the silver compound is decomposed as it is as a liquid film, a dense, uniform and continuous silver coating can be formed, and a silver coating with high conductivity and high strength can be obtained. Also,
Since the decomposition temperature is 200 ° C. or lower and the heat treatment temperature can be lowered, a base material having low heat resistance can be used, and the restriction of the base material is relaxed. Here, the decomposition temperature is the temperature at which the weight of the silver compound starts to decrease when the temperature is increased at a temperature increase rate of 10 ° C./min using a thermogravimetric differential thermal analyzer. Also,
In the conductive composition of the present invention, the silver compound has 10 carbon atoms.
The above tertiary fatty acid silver compound is preferable. While many fatty acid silver compounds have melting points higher than the decomposition temperature, tertiary fatty acid silver compounds having 10 or more carbon atoms have a melting point lower than the decomposition temperature and melt and liquefy before decomposition.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The conductive composition of the present invention has a decomposition temperature of 200 ° C. or lower and contains a silver compound having a melting point in a temperature region lower than the decomposition temperature. As such a silver compound, a tertiary fatty acid silver compound having 10 or more carbon atoms can be used. Examples of the tertiary fatty acid silver compound having 10 or more carbon atoms include silver neodecanoate and silver salt of Equacid 13 (manufactured by Idemitsu Petrochemical). Here, the tertiary fatty acid silver compound is a silver salt of a tertiary fatty acid. Further, the tertiary fatty acid is an aliphatic carboxylic acid in which a carbon atom bonded to a carboxyl group is not bonded to a hydrogen atom, and examples thereof include pivalic acid, neononanoic acid, neodecanoic acid, equacid 9 (manufactured by Idemitsu Petrochemical Co., Ltd. ), Equacid 13 (manufactured by Idemitsu Petrochemical), and the like. Many of the tertiary fatty acid silver compounds have a decomposition temperature of 200 ° C. or lower, and those having 10 or more carbon atoms have a melting point lower than the thermal decomposition temperature. The tertiary fatty acid silver compound can be produced by a metathesis method which is a general method for producing metallic soap. For example, the tertiary fatty acid is neutralized with sodium hydroxide to form a sodium salt, and this sodium salt is mixed with an aqueous silver nitrate solution to undergo a metathesis reaction to form a water-insoluble salt, and a tertiary fatty acid silver compound is precipitated and recovered.

The silver compound may be dissolved in a solvent.
The solvent is not particularly limited as long as it can dissolve the silver compound. For example, when the silver compound is a tertiary fatty acid silver compound, any solvent that can dissolve the tertiary fatty acid silver compound may be used. It can be freely selected according to the application and curing conditions of the product. Examples of the solvent that dissolves the tertiary fatty acid silver compound include hydrocarbon solvents, intermediate alcohols, higher alcohols, glycol ethers, and the like. When the silver compound is dissolved in a solvent, the ratio of the silver compound and the solvent is not particularly limited as long as the silver compound is dissolved, but in consideration of the solvent's solvency, the viscosity of the resulting conductive composition, and printability. It is preferable to determine the appropriate ratio. Further, there is no particular limitation on the device or method used for dissolving the silver compound in the solvent.

The conductive composition may contain various additives such as a thickener for the purpose of improving coating or printing properties. However, when the additive is contained in the conductive composition, when the silver coating is formed, the additive may remain between the silver particles and reduce the conductivity of the silver coating. 20% by weight or less of the compound is preferable, and 5% by weight or less is preferable.

Next, the method for forming the conductive film of the present invention will be described. In this forming method, first, the conductive composition is appropriately printed on a substrate by a coating means or the like to form a coating film. Here, examples of the coating means include screen printing and gravure printing. Then, the coating film is heat-treated at 100 to 200 ° C. During this heat treatment, when the temperature of the coating film becomes equal to or higher than the melting point of the silver compound, the silver compound becomes liquid, and when further heated and the temperature becomes equal to or higher than the decomposition temperature,
The silver compound is thermally decomposed to deposit silver and form a silver film. The heat treatment is preferably performed at a high temperature with 200 ° C. as the upper limit and for a short time. When the temperature is high, the amount of organic residue is small, and thus the conductivity can be increased. In addition, when the heat treatment is performed for a short time, it is possible to prevent deterioration of the physical properties of the base material due to heat. The specific temperature of the heat treatment is a thermal decomposition temperature of the silver compound or a temperature close thereto, and for example, in the case of silver neodecanoate, a heating temperature of 150 ° C. and a heating time of 30 minutes are sufficient, and a maximum temperature of 200 ° C. 30 minutes. Also,
Even at a temperature equal to or lower than the melting point of the silver compound, the silver compound melts and decomposes near the melting point, so that a silver film having high conductivity can be formed by taking sufficient time. For example, when a silver salt of Equacid 13 (melting point 110 ° C.) is used, a heat treatment temperature of 100 ° C. and a treatment temperature of 120 minutes can provide a silver coating having a volume resistivity value of 10 ⁻⁶ Ω · cm order. it can.

According to such a forming method, when the coating film made of the above-mentioned conductive composition is heated, the film is liquefied as it is, and when the heating is continued, the silver compound is thermally decomposed as a liquid film. , A film of silver particles is formed. In the silver coating which is the conductive coating thus formed, the deposited silver atoms are fused together, and are dense, uniform and continuous, so that the conductivity and the strength of the coating are high. Especially, 20
The conductivity when heated at 0 ° C. is almost the same as that of metallic silver. Further, in this forming method, since the heat treatment temperature is 200 ° C. or lower, a base material having low heat resistance can be used. That is, plastic can be used as the substrate. Also, glass, ceramics, and enamel can be used.

Since the silver compound is decomposed by irradiation with ultraviolet light (UV) or infrared light (IR), the coating film may be irradiated with UV or IR to form a silver coating film. Also,
The heat treatment and the irradiation of UV or IR may be simultaneously performed to form a silver film.

The conductive coating film of the present invention has characteristics other than high conductivity. That is, since the silver is dense, the surface of the conductive coating on the substrate side has a mirror surface with a rich metallic luster. Therefore, the back surface of the transparent substrate such as glass or plastic film or the substrate side surface of the conductive coating peeled from the substrate is used as a mirror with high reflectance for household use.
It can be used for industrial purposes. For example, it can be used as a reflector of a resonator of a laser device.

[0014]

EXAMPLES The present invention will be described in more detail below with reference to Examples 1 to 3 and Comparative Examples 1 to 3. In addition, Example 1
The decomposition temperature and melting point of the fatty acid silver compounds used in Comparative Example 3 and Comparative Examples 1 to 3 were measured by the following methods. (Decomposition temperature) TG-DTA (manufactured by Shimadzu Corporation) is used,
The fatty acid silver compound was heated at a temperature rising rate of 10 ° C./min, and the temperature at which the weight started to decrease was taken as the decomposition temperature. (Melting point) The fatty acid silver compound was allowed to stand for 10 minutes in a hot air circulation drying furnace set to a predetermined temperature, and the temperature at which it was melted was taken as the melting point. The temperature was raised from 100 ° C at 10 ° C intervals.

(Example 1) A tertiary fatty acid silver compound
Dissolve 10.0 g of silver odecanoate in 10.0 g of toluene
Thus, a conductive composition was obtained. The viscosity of this conductive composition is 0.
It was 05 dPa · s / 23 ° C. This conductive composition
Coating on polyethylene terephthalate (PET) film
To form a coating film, and heat the coating film at 150 ° C for 30 minutes.
Processed and heat decomposed silver neodecanoate to form a silver film.
Let The electroconductivity of the obtained silver coating is 0.
08 Ω / cm², Volume resistivity of 8.0 × 10^-6Ω
・ It was cm. In addition, heat treatment at 200 ° C for 30 minutes
The obtained silver coating is 3.5 × 10 ^-6 Ω · cm, metal
Volume resistivity of silver 1.6 × 10^-6Value close to Ω · cm
Became.

[0016]

[Table 1]

Example 2 The silver neodecanoate of Example 1 was
Ex Acid 13 (made by Idemitsu Petrochemical) except changed to silver
A silver coating was obtained in the same manner as in Example 1. Conductivity at this time
The viscosity of the composition was 0.05 dPa · s / 23 ° C.
Sheet resistance of silver coating obtained by heat treatment at 150 ℃ for 30 minutes
Value is 0.085Ω / cm² And the volume resistivity is
8.5 x 10 ^-6It was Ω · cm. Also, at 200 ° C
The silver film obtained by heat treatment for 30 minutes has a size of 3.7 × 10.^-6 Ω
・ It was cm.

Example 3 First, hydroxypropylcellulose (HPC), which is a thickener, was dissolved in 2-methyl-2-butanol, which was a solvent, to a concentration of 1% by weight. Then, 3.0 g of silver neodecanoate was dissolved in this solution to obtain a conductive composition. The viscosity of the conductive composition was 5 dPa · s because the added HPC exerted a thickening effect.
It was / 23 ° C. This conductive composition was applied to a polyethylene terephthalate (PET) film,
After heat treatment at 0 ° C. for 30 minutes, silver neodecanoate was decomposed by heat to form a silver film. The sheet resistance of the obtained silver coating was 0.1 Ω / cm ² , and the volume resistivity was 10.0 × 10.
It was ⁻⁶ Ω · cm. The silver coating obtained by heating at 200 ° C. for 30 minutes had a density of 3.8 × 10 ⁻⁶ Ω · cm.

Comparative Example 1 A silver coating was formed in the same manner as in Example 1 except that the silver neodecanoate of Example 1 was changed to silver 2-ethylhexanoate which is a secondary fatty acid compound. , Hardly decomposed at a heat treatment temperature of 150 ° C,
Since it was not silvered sufficiently, conductivity was not exhibited.
Further, when heat-treated at 200 ° C., silver was deposited in the form of particles and a continuous film was not formed, so that conductivity was not exhibited.

[0020]

[Table 2]

Comparative Example 2 An attempt was made to form a silver coating in the same manner as in Example 1 except that the silver neodecanoate of Example 1 was changed to silver oleate which is a primary fatty acid silver compound. At 150 ° C., it was hardly decomposed and was not sufficiently silverized, so that conductivity was not exhibited. Also, 2
When heat-treated at 00 ° C., silver was precipitated in the form of particles and a continuous film was not formed, so that conductivity was not exhibited.

Comparative Example 3 A silver coating was formed in the same manner as in Example 1 except that silver neodecanoate of Example 1 was changed to silver neononanoate having a carbon number of 9 which is a tertiary fatty acid silver compound. At both heat treatment temperatures of 150 ° C. and 200 ° C., silver was deposited in the form of particles and a continuous film was not formed, so that sufficient conductivity could not be obtained.

In Examples 1 to 3, the decomposition temperature is 200 ° C. or lower, and the silver compound having a melting point in the temperature range lower than the decomposition temperature is contained. Therefore, a heat treatment at 200 ° C. or lower forms a highly conductive silver film. Was done. In particular, when heat-treated at 200 ° C., a conductive silver film similar to metallic silver was obtained.
In addition, in Example 3, since the thickener was contained, the thickener was present between the silver particles, and thus the conductivity was slightly lower than that of Example 1, but The coatability was excellent. On the other hand, in Comparative Examples 1 to 3, since the silver compound had no melting point, a silver film having high conductivity could not be obtained by the heat treatment at 200 ° C. or lower.

[0024]

EFFECTS OF THE INVENTION According to the present invention, when heated, it melts and becomes a liquid before it is thermally decomposed, so that a granular lump is not formed and a dense, uniform and continuous silver coating is formed. Can be made. Therefore, a silver coating having high conductivity and high coating strength can be obtained. Also, the decomposition temperature is 200
Since the temperature is not higher than 0 ° C. and the heat treatment temperature can be lowered, a plastic material having low heat resistance can be used as a base material, and thus it can be applied to a wide range of applications. A base material having low heat resistance can be used, and restrictions on the base material are relaxed.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01B 13/00 503 H01B 13/00 503C // H05K 3/12 610 H05K 3/12 610B (72) Inventor Masafumi Ito 5-13-1, Sakurada, Washimiya-cho, Kita-Katsushika-gun, Saitama Prefecture F-term in Development Laboratory, Fujikura Kasei Co., Ltd. AA01 AB11 AD10 AE10 5G307 GA06 GC02

Claims (5)

[Claims] 1. A conductive composition having a decomposition temperature of 200 ° C. or lower and containing a silver compound having a melting point in a temperature region lower than the decomposition temperature. 2. The conductive composition according to claim 1, wherein the silver compound is a tertiary fatty acid silver compound having 10 or more carbon atoms. 3. The conductive composition according to claim 1, which contains a thickener. 4. Coating the conductive composition according to claim 1 on a substrate to form a coating film, and thermally treating the coating film at 100 to 200 ° C. A method for forming a conductive coating film, comprising: 5. A conductive coating film, which is formed by heat-treating the conductive composition according to claim 1 at 100 to 200 ° C.