JPH0139463B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses a fine metal powder (hereinafter abbreviated as metal powder), mainly Cu, and other metal powders as a conductive material, and a hydroquinone derivative in a thermosetting resin as a binder (hereinafter abbreviated as a binder). The present invention relates to a conductive paint characterized by using a paint in which the additive is dissolved in a suitable solvent, and further comprising adding a small amount of a natural oil-based organic fatty acid to the binder as an auxiliary additive. Conductive paints are currently used in various fields, but it is well known that they are particularly used in electronic components. Its uses are wide-ranging, such as as a substitute for jumper wires on printed wiring boards, and as terminals for printed resistors using printed wiring boards. The most important condition for a conductive paint is that when the paint is used to form part of an electrical circuit by printing, spraying, brush painting, etc., its surface specific resistance (hereinafter abbreviated as specific resistance) ρ' The value should be 1Ω/□ or less, preferably 0.1Ω/□. Metals that satisfy these conditions are generally called noble metals, and powders of Au and Ag are mainly used.
Especially in terms of price, Ag powder is the main ingredient, and powders such as Au and Pt are only occasionally used in combination. As is well known, Cu is second only to Ag in terms of volume resistivity ρ.
However, it seems that there are still no conductive paints using Cu powder that have been put into practical use not only in Japan but also in the United States, West Germany, and other countries. However, recently it has become the second raw material after Au.
The price of Ag has increased significantly, and as a result, Ag
The price of conductive paints using powder increased several times, and the impact on the electronic parts industry became extremely large. For this reason, research into conductive paints using Cu powder has become of great significance, and much research has been carried out, but Cu conductive paints, which can be used as a substitute for Ag conductive paints, have not yet been commercialized. Next, using Cu powder as a conductive powder,
A conductive paint using a general thermosetting resin as a binder will be briefly described. When general thermosetting resins undergo polycondensation to form giant resin molecules with a three-dimensional network structure, H ₂ O is generally produced as a reaction product, and other by-products may be produced depending on the type of resin. It is widely known that they will leave. In this case, a thin layer of copper oxide is formed on the surface of the highly active Cu powder by the interaction of the by-products generated by the separation with heat. In addition, the smaller the particle size of the Cu powder, the more activated it becomes, and when left in the air, it quickly captures oxygen and forms a thin layer of oxide on the surface. When the resin is cured, its volume resistivity becomes even larger. For this reason, it has generally been difficult to obtain a low-resistance paint when metal powder other than noble metals is used. From the above, it is presumed that in order to manufacture a low-resistance conductive paint using metal powder other than noble metal powder, it is necessary to select a thermosetting resin that satisfies the following two conditions. (i) It should not oxidize the metal powder when stored as a paint, but rather have a reducing property. (ii) When sintering paint at high temperatures, it absorbs oxygen and undergoes polymerization or condensation reactions. That is, the first condition is to prevent the metal powder in the paint from being oxidized during storage as a conductive paint, and the second condition is to prevent printing using the conductive paint.
When electrodes, electrical circuits, etc. are formed by brush painting, spraying, etc. and sintered at high temperatures, the metal powder in the coating film is not oxidized, even if the powder has a thin oxidized layer on the surface. This is a necessary condition for its reduction to form a low-resistance conductive film or layer. The main inventions based on the above idea are as follows. (1) Japanese Patent Application No. 50-17392 (Conductive composition) (2) Japanese Patent Application No. 50-39227 (Conductive composition) However, the above invention, as disclosed in the detailed description of the invention, The value of resistivity ρ' is still too large to be used as a substitute for Ag paste. It should be noted here that adding a reducing agent or the like to the metal powder or binder for the purpose of preventing oxidation may deteriorate the moisture resistance, heat resistance, etc. of the paint film when the curing reaction of the paint is completed. is common. Therefore, it is necessary to avoid mixing or filling reducing agents etc. for the purpose of preventing oxidation. After examining the conditions (i) and (ii) above in detail, the inventor found that in addition to the above two conditions, other conditions are necessary in order to further reduce the value of ρ'. did. As a result, it was confirmed that the above two conditions are necessary conditions, but not sufficient conditions. Through this research, the present inventors came to invent a Cu conductive paint that can be used as a substitute for Ag conductive paint. That is, an object of the present invention is to provide a conductive paint having excellent properties using other metal powders, mainly Cu powder, in place of the currently used Ag conductive paint. In order to achieve the above object, the conductive paint according to the present invention is produced by adding a small amount of organic fatty acid and a metal powder as a conductive substance to a paint made by dissolving a thermosetting resin with a hydroquinone derivative in an appropriate solvent. It is characterized by being formed by dissolving and dispersing it. Next, the configuration of the present invention will be explained in detail. The present invention is a further improvement of the invention of Patent Application No. 129,115 (hereinafter referred to as the "previous application") filed on September 19, 1980 by the same applicant. Therefore, I will first give a very brief summary of the previous application. Hydroquinones are basic units for synthesizing quinone-based oxidized or reduced resins. In general, most of them are colorless crystals and easily oxidized. As is well known, it is widely used in photographic chemicals, preservatives, etc. The structures of hydroquinones are illustrated below.

【formula】

【formula】

【formula】

【formula】

【formula】

[Formula] (A): pyrocatechol (D): pyrogallol (B): hydroquinone (E): chlorogloscin (C): resorcinol (F): gallic acid When the above hydroquinones are added to other polymer resins, a curing reaction occurs. is prevented. The reaction will be illustrated using the above-mentioned pyrocatechol as an example. Equation (1) shows a reversible reaction regarding oxidation and reduction of pyrocatechol, and equation (2) shows an example of the reaction between a resol resin (phenolic resin) and pyrocatechol. (2)
As is clear from the formula, in such a case, a macromolecule with a three-dimensional network structure is not formed. The reaction of formula (2) is similar when added to other resins. While researching the physicochemical properties of hydroquinones, the inventor of the previous application, who is the same as the present inventor, discovered that he had created a special derivative of hydroquinones, and by simply adding the derivative to another resin and causing a heating reaction, the functional group could be created. We have discovered that a macromolecule with a three-dimensional network structure can be formed without any addition, that is, the polycondensation reaction can be completed. This discovery forms the basis of the previously filed invention. Next, we will discuss pyrocatechol, a hydroquinone, as an example. (A) When pyrocatechol is dispersed in a solution of copper oleate, pyrocatechol derivatives are obtained by the catalytic action of Cu ⁺ ions in the solution. That is, the following equation (3) is obtained. The structure of R varies depending on the reaction conditions, i.e., ambient temperature, humidity, type of organic solvent used as a diluent, type of fatty acid and metal ion, etc.
Without going into detail here, those having the chemical structure shown in formula (3) will simply be defined as pyrocatechol derivatives. (B) A case where the pyrocatechol derivative is reacted with another resin will be described. As an example, when the above-mentioned phenolic resin, that is, resol type resin, is dissolved and heated, the reaction proceeds as shown in the following equation,
Here, a macromolecule with a three-dimensional network structure is formed. The reaction of formula (4) occurs similarly when epoxy resin, melamine resin, etc. are used. In the formula (4), X is mainly H ₂ O. Even when using general hydroquinone derivatives, the same reaction as described above occurs, and those that have reactive groups other than OH groups or those that have added reactive groups cause polycondensation reactions with other resins, resulting in the formation of a three-dimensional network structure. Becomes a giant molecule. It has been described above that hydroquinone derivatives react with other resins and are thermally cured to form macromolecules. Next, we will describe the characteristics of a conductive paint that uses a thermosetting resin with the above-mentioned pyrocatechol derivative added as a binder and Cu powder as a conductor. Since it is not possible to obtain a conductive coating material with good characteristics if a resin that cures at room temperature is used, a thermosetting resin whose curing temperature is at least 110° C. or higher is used. (1) Oxygen absorption reactions occur rapidly at high temperatures. As a result of thermogravimetry and differential thermal analysis, pyrocatechol derivatives rapidly turn into quinones when the ambient temperature reaches 115°C or higher, absorbing large amounts of oxygen from the atmosphere. The outline is shown below. On the other hand, as shown in equation (4), this type of quinone reacts with the thermosetting resin to advance radical polymerization, forming a dense polymer resin layer on the surface of the conductive paint film. In the case of the reaction of formula (5), if there is a thin oxide film on the surface of the Cu powder, it will be reduced at the same time, and after curing it will be covered with a dense film and the oxidation reaction will not proceed. (2) Cu powder is not oxidized by high-temperature heating. When a pyrocatechol derivative is added to a thermosetting resin, the activation energy (endothermic reaction...minus) associated with oxidative polymerization at high temperature is
This is much larger than the activation energy (exothermic reaction...plus) during thermal oxidation of Cu, so
This is because oxidation of Cu is prevented. (3) Shows strong reducing properties when heated at high temperatures. As mentioned above, when a thermosetting resin containing a pyrocatechol derivative is heated to high temperatures, the surface hardens and forms a dense film, making it extremely difficult for oxygen to permeate, resulting in an oxygen-deficient interior. Therefore, the activated pyrocatechol derivative advances the curing reaction by absorbing oxygen from the thin oxide layer on the surface of the Cu powder. In other words, strong reducing properties are produced. (4) Soluble in many organic solvents. Pyrocatechol derivatives have an OH group as shown in formula (3), so they dissolve well in many organic solvents. On the other hand, since it does not cause a polycondensation reaction when used alone, when combined with other thermosetting resins, a paint with excellent properties can be obtained, and the structure does not deteriorate during storage. (5) The properties as a conductive paint do not deteriorate during storage. It has a pot life of over a year if moisture is prevented from entering. It has a pot life of more than a month even when exposed to room temperature and humidity. (6) The contact resistance of metal powder decreases due to the curing reaction. As mentioned in Section 3, when the metal powder is cured at high temperature, the oxide layer covering the surface of the metal powder is reduced, so that the contact resistance becomes small. In addition, thermosetting resins to which pyrocatechol derivatives are added produce very unique effects upon curing. In other words, if a macromolecule with a three-dimensional network structure is formed during curing, the cured molecule will have a diameter of
The result is a dense and robust structure with a spherical orientation of 0.2 μm to 50 μm. Therefore, the metal powder that fills the gaps between molecules is tightly bound, thus increasing the contact area between the binders, and as a result, the conductivity of the metal powder is further improved. (i) and (ii) above, this property is necessary to obtain good conductivity.
In addition to condition (iii), this condition is considered to be a sufficient condition. In the previously filed invention based on the above research,
The structure and effects of the invention will be described in detail with reference to examples, and even if Cu powder is used as the conductive material,
It was stated that a paint comparable to the conventional conductive paint using Ag powder could be obtained. However, the conductive paint according to the invention of the previous application cannot be said to have sufficient moisture resistance. In other words, the resistance of a conductor printed on a Bakelite laminate using the paint and sufficiently cured is set as _R0 , and this is placed in a constant temperature bath at a temperature of 60℃ and a relative humidity of 95%RH, and the resistance change rate δR is calculated as a function of time. When measured, the result is curve A in Figure 1. Here, δR=R _t −R ₀ /R ₀ ×100% (6) R _t in equation (6) is the resistance value at the time of measurement. In other words, when using the conductive paint according to the invention of the previous application, in order to sufficiently maintain its moisture resistance, it is necessary to apply a method such as applying a paint with excellent moisture resistance on the coating film. . Next, the structural features of the present invention will be explained in detail. When a small amount of organic fatty acid is added to the conductive paint using the hydroquinone derivatives of the previous application, the fatty acid will coat the resin molecules and metal powder in the conductive paint. Therefore, when a thin coating film is made by printing, brushing, spraying, etc. using this paint, and this is sintered at a temperature of 110℃ to 170℃, an extremely thin coating film is formed on the surface of the coating. Ru.
Similarly, inside the paint film, a thin film of fatty acid is formed on the surface of resin molecules and metal powder. That is, if such a coating film structure is adopted, as a result, it becomes difficult for water molecules to penetrate into the coating film even under high humidity. In other words, it will be understood that the moisture resistance is significantly improved. As will be described later, the effect is remarkable. However, as is clear from the above explanation,
The fatty acid thin film formed on the surface is an insulating film and has high insulation resistance. Therefore, as the film thickness increases, the resistivity of the conductive paint increases rapidly. For this reason, the amount of organic fatty acid added needs to be kept as small as possible to improve moisture resistance. That is, the optimum value must be determined through experiments, taking into account the balance between resistivity and moisture resistance. Examples will be further described in detail below. Example 1 The pyrocatechol derivative shown by formula (3) was added to an epoxy-melamine resin with excellent moisture resistance and heat resistance in an amount of 60% to 100% of the pure resin amount (weight) of the resin.
The resin added at the ratio of is called EM resin for short.
(The same applies below) EM resin...16% by weight Fine Cu powder...80 Oleic acid; C ₁₇ (CH ₂ ) ₇ COOH...4 When producing, for example, a conductive paint for printing with the above composition, first EM resin is used. is dissolved in a suitable solvent, then Cu powder with a particle size of 10 μm or less is dispersed, and oleic acid is added to this and mixed well to create a paint suitable for screen printing. Next, a PC board (phenol laminate) on which Cu thin film electrodes were formed using a nylon screen and chemical etching.
A zigzag pattern with a film thickness of 50 μm, width of 2 mm, and length of 372 mm was printed on top, and this was sintered and hardened in a constant temperature bath at 160° C. for 30 minutes. As a result of measuring the resistance value of the samples made in this way, sample 10
The average value was 3.82Ω, and the variation was extremely small. Therefore, the specific resistance ′ (average value) is ′=3.82×2/372=0.021Ω/□. This value is comparable to that of conventional Ag paints. Next, a moisture resistance test was conducted using the method described above, and the resistance change rate ΔR was determined using equation (6). The results are shown by curve B in FIG. In this case as well, the variation in the values of the 10 co-test samples was small. It is clear that the properties are significantly improved. The content of oleic acid can be used in the range of 2 to 8% by weight, assuming that the weight % of the resin is constant at the above value. The 4% value is the center value of the neighborhood that gives the minimum ρ'. Example 2 EM resin...16% by weight Fine Cu powder...80 Linoleic acid; _C17H31COOH ...4 The above materials were treated in exactly the same _manner as described in Example 1 to make them conductive. A paint was made, and a resistance sample was made using the same method, and the specific resistance ρ' was determined from the resistance value. As a result, the following values were obtained as the average values of 10 samples. Note that the variation was small. '=0.023Ω/□ This value is comparable to that of general Ag paint. Next, using this sample, a moisture resistance test was conducted under the same conditions as in Example 1. As a result, the resistance change rate δR after 200 hours was (12 to 13)%, which was almost the same result as in Example 1. It was hot. The range of the linoleic acid content and the content value that provides the minimum ρ' are almost the same as in Example 1. Example 3 EM resin...16% by weight Fine Cu powder...80 _Linolenic acid; _C17H29COOH ...4 The above materials were treated in exactly the same manner as described in Example 1 to make them conductive. A paint was made, a resistance sample was made in the same manner, and the specific resistance was determined from the resistance value. As a result, the following values were obtained as the average values of 10 samples. Note that the variation was small. '=0.019Ω/□ This value is comparable to that of general Ag paint. Next, using this sample, a humidity test was conducted under the same conditions as in Example 1. As a result, the resistance change rate δR after 200 hours was (11 to 13)%, which was almost the same as in Example 1. The results were outstanding. In addition to the above-mentioned oleic acid, linoleic acid, and linolenic acid, stearic acid, quinolinic acid, maleic acid, abietic acid,
Organic fatty acids such as gallic acid can be used, but all of them have the disadvantage that the rate of change in specific resistance becomes large in terms of moisture resistance. Next, the effects of the present invention will be briefly described. (a) By adding a small amount of organic fatty acid to the conductive paint using a hydroquinone derivative according to the previously filed invention, the moisture resistance of the conductive paint could be significantly improved. (b) As is clear from the above, the conventional
A Cu conductive paint with comparable properties to Ag conductive paint was obtained. (c) In Cu conductive paint, the Ag migration phenomenon, which is a major drawback that cannot be avoided in the case of Ag conductive paint,
So-called Ag migration (Silver
Migration) issues were resolved at once. (d) Compared to Ag conductive paint, the price is extremely low.

[Brief explanation of drawings]

FIG. 1 is a graph showing the moisture resistance properties of the conductive paint according to the invention of the previous application and the present invention.

Claims (1)

[Scope of Claims] 1 A small amount of organic fatty acid and a fine metal powder (hereinafter referred to as metal powder) as a conductive substance are added to a paint made by adding a hydroquinone derivative to a thermosetting resin and dissolved in an appropriate solvent. A conductive paint using a hydroquinone derivative, which is characterized by being dissolved and dispersed. 2. A conductive paint using a hydroquinone derivative according to claim 1, characterized in that oleic acid is used as the organic fatty acid according to claim 1. 3. A conductive paint using a hydroquinone derivative according to claim 1, characterized in that linoleic acid is used as the organic fatty acid according to claim 1. 4. A conductive paint using a hydroquinone derivative according to claim 1, characterized in that linolenic acid is used as the organic fatty acid according to claim 1. 5. A conductive paint using a hydroquinone derivative according to any one of claims 1 to 4, characterized in that Cu powder is used as the metal powder according to claim 1.