JPH0135025B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a conductive material characterized by using a fine metal powder (hereinafter abbreviated as metal powder) as a conductive material and a thermosetting resin with a hydroquinone derivative added as a binding material (hereinafter abbreviated as binder). It is related to paint. 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 skyrocketed 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 depending on the type of resin, other by-products may also be produced. It is widely known that the US is leaving the country. 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 (Japanese Patent Publication No. 55-10081) (conductive composition) (2) Japanese Patent Application No. 50-39227 (Japanese Patent Publication No. 58-49967) (conductive composition) However, the above-mentioned As disclosed in the detailed description of the invention, the value of specific resistance 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, the purpose of the present invention is to replace the current Ag conductive paint.
The object of the present invention is to provide a conductive paint with excellent properties. In order to achieve the above object, the conductive paint according to the present invention is characterized in that it is made of a binder made of a thermosetting resin and a hydroquinone derivative, and metal powder is dispersed therein as a conductive substance. Next, the configuration of the present invention will be explained in detail. First, the outline of the reaction of hydroquinones will be explained. 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. (A): Pyrocatechol (D): Pyrogallol (B): Hydroquinone (E): Phloroglossin (C): Resorcinol These hydroquinones exhibit reversible reactions with respect to oxidation and reduction. In general, hydroquinones and quinone-based oxidation and reduction resins are sometimes used as inhibitors of radical and ionic reactions of other polymeric resin monomers, and prevent the polymerization of the polymeric resins. Therefore, when hydroquinones are added to other polymeric resins, the curing reaction is inhibited. 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. In other words, in general, when hydroquinones are reacted with other resins, unless a functional group is added separately from the other resins, radical polymerization with the resin proceeds in a chain reaction, resulting in a three-dimensional giant assembly. It does not lead to the formation of knowledge. While researching the physicochemical properties of hydroquinones, the present inventor discovered that once a special derivative of hydroquinones was created, the derivative could be added to other resins and reacted with heat, without the need to separately add the above-mentioned functional groups. ni, 3
We discovered the fact that a macromolecule with a dimensional network structure is formed, that is, the polycondensation reaction is completed. This discovery forms the basis of the present 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. Here, R is R=-(CH) _l- (CH ₂ ) _n -C _o H _2o+1 (A) or R=-COO-(CH) _l - CH containing an alkyl group C _o H _2o+ 1 represented by (CH ₂ ) _n −C _o H _2o+1 (B),
Generally, it has a CH ₂ chain structure. In addition,
The values of m and n vary depending on the reaction conditions, the type of organic solvent used as a diluent, fatty acids, metal ions, etc., and it is currently difficult to produce constant A and B, so perfect reproducibility cannot be achieved. Therefore, it is not possible to produce formula (a) or (b) of formula (3). In formula (3), structure (a) is generally used. (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. (4)X in the formula
is mainly H ₂ O. Even when using general hydroquinone derivatives, the same reaction as above is shown,
Those that have reactive groups other than OH groups or those that have been added will cause polycondensation reactions with other resins, resulting in
It becomes a macromolecule with a dimensional network structure. It has been described above that hydroquinone derivatives react with other resins and are thermally cured to form macromolecules. Furthermore, if we look at formulas (3) and (4) in the specification, we can see that even if other pyrocatechol derivatives such as hydroquinone, resorcinol, pyrogallol, etc. are used in addition to pyrocatechol, derivatives corresponding to formula (3) can be obtained. , therefore, it will be easily understood that macromolecules corresponding to formula (4) can be obtained. For example, another example using hydroquinone is shown below. When dispersed in a solution of copper oleate in the same manner as above, In formula (3'), structure (a) is common. (3′)
The equation corresponds to equation (3). Next, when the hydroquinone derivative is dissolved in a phenolic resin, that is, a resol type resin and heated in the same manner as described above, the reaction proceeds as follows to form a macromolecule having a three-dimensional network structure. Equation (4') corresponds to Equation (4), and X is mainly H ₂ O like X in Equation (4). 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 paint with good characteristics if a cold-curing resin 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 reaction (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 oxidation, it will be covered by a dense film and the oxidation reaction will not proceed. (2) Cu powder is not oxidized by high-temperature heating.
Cu powder (particle size 10μm or less) begins to oxidize at 160℃, and when the temperature reaches 235℃, the oxidation reaches the inside.
The oxidation reaction of Cu is an exothermic phenomenon. That is, the activation energy is positive. On the other hand, when a pyrocatechol derivative is added to a thermosetting resin and heated, the curing reaction starts at 110°C, and the temperature rises to 170°C to 180°C.
The reaction is completed. The curing reaction is an endothermic phenomenon. That is, the activation energy in this case is negative. Therefore, in the resin in which Cu powder is dispersed, even if the curing temperature reaches 160°C or higher, the activation energy of Cu is absorbed as curing energy of the resin, and the oxidation reaction is hindered. ₂ Unable to become O. That is, it does not oxidize even at high temperatures. Even if the temperature rises further, the surface of the binder resin has already hardened, forming a dense film and cutting off the supply of oxygen, so the oxidation of Cu does not proceed. (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, in order to advance the curing reaction, the activated pyrocatechol derivative absorbs oxygen from the thin oxide layer on the surface of the Cu powder and attempts to complete the polycondensation reaction with the thermosetting resin. Therefore, the surface oxidation layer of the Cu powder is reduced and the conductivity of the Cu powder is improved. (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. Generally, pyrocatechol derivatives do not turn into quinones at room temperature, so when added to thermosetting resins as binders for conductive paints, no curing reaction occurs. However, the molecular chains of thermosetting resins may be severed by OH groups in high humidity environments, so as mentioned above, it is desirable to completely block humidity during long-term storage. (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 temperatures, the oxide layer covering the surface of the metal powder is reduced, so the contact resistance is reduced. Additionally, 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. Next, examples will be described in more detail. Example 1 A pyrocatechol derivative represented by formula (3) was added to an epoxy-melamine resin having excellent moisture resistance and heat resistance at a ratio of 60 parts to 100 parts of pure resin (weight). A conductive paint suitable for screen printing was created by dispersing Cu powder with a particle size of 10 μm or less and adding an appropriate solvent. According to the results of experiments, the appropriate amount of hydroquinone derivatives to be added is generally in the range of 30 to 70 parts based on 100 parts of pure resin, even when other thermosetting resins are used. Next, using the conductive paint, apply a nylon screen to the PC board (phenol laminate) on which Cu electrodes are formed by chemical etching.
A zigzag pattern of 50 μm, width 2 mm, and length 372 mm was printed. This was sintered and hardened for 30 minutes in a constant temperature bath at 160°C. The resistance value of the sample thus prepared was measured, and the specific resistance ρ' (Ω/□) was determined from the measured value. The results are shown in FIG. The horizontal axis is the Cu content f, which is given by f=m/r+m×100% (6) where r is the amount of pure resin in the paint and m is the weight of Cu powder. According to the figure, when the Cu content is around 80%, ρ′ is
A minimum value of 0.2Ω/□ was obtained. It can be seen from the figure that a range of f of 74% to 86% can be used satisfactorily.
According to the experimental results, the Cu content falls within this range regardless of the thermosetting resin used. In this case, the lowest value of resistivity ρ′ obtained is
It was 0.2Ω/□ (see line 4 from page 17 and Figure 1), but when no pyrocatechol derivative was added, the average value of the lowest specific resistance ρ was 120Ω/
It was □. Therefore, when the pyrocatechol derivative is not added, the resistance value is 120 (Ω/□)/0.2 (Ω/□) = 600, that is, 600 times larger than when it is added. It will be clear how effective the addition of pyrocatechol derivatives is. Next, the sample was placed in a constant temperature bath at 100°C and a heat resistance test was conducted. The results are shown in Figure 2. The number of samples tested was 10. In the figure, ρ′ ₀ represents the initial resistivity, and Δρ′ represents the change obtained by subtracting ρ′ ₀ from the specific resistance at the time of measurement after the start of the test. The curve is the rate of change △ρ′/
It connects the average values of ρ′ ₀ , and the arrow indicates the range of dispersion. Next, since the conductive film using the conductive paint according to the present invention cannot be said to have sufficient moisture resistance, adding a very small amount of natural oil-based fatty acids such as oleic acid to improve moisture resistance will improve the moisture resistance. can get. FIG. 3 shows the moisture resistance when the moisture resistance is improved as described above. Test conditions were temperature 60℃ and relative humidity 93%.
It was set as RH. In the figure, ρ′ ₀ is the initial resistivity, △
ρ′ represents the change obtained by subtracting ρ′ ₀ from the specific resistance at the time of measurement. The curve connects the average value of the rate of change △ρ′/ρ′ ₀ (the number of samples tested is 10), and the arrow indicates the range of variation. According to the figure, the influence of humidity reaches a constant value of approximately 11% after approximately 200 hours, and is hardly affected thereafter. From the above test results, it can be said that the heat resistance and moisture resistance are sufficient. Although this example uses a pyrocatechol derivative, almost the same results can be obtained when other derivatives are used. For example, hydroquinone,
Even when a derivative such as resorcinol is used, the lowest value of resistivity is (0.1 to 2.0) Ω/□ (excluding unsaturated polyester resin), and other characteristics are almost the same as in this example. There is no difference. This will be omitted as it will be complicated. Next, although this example used an epoxy-melamine resin as the thermosetting resin, similar results can be obtained using other thermosetting resins. For example, the minimum value of resistivity ρ' when using typical resins such as phenol and epoxy is shown below in the form of a table. In that case, heat resistance properties,
The moisture resistance characteristics and the like are not much different from those shown in FIGS. 2 and 3, so they are omitted for the sake of brevity.

[Table] Example 2 An experiment was conducted on metal powder other than Cu with a particle size of 10 μm or less. The preparation of the sample is exactly the same as in Example 1, so the explanation will be omitted. The first
The table shows the test results.

[Table] According to Table 1, in some cases other than Ag
It is thought that metal powders such as Ni, Cr, and Mo can be used. In this case, in order to improve moisture resistance, a small amount of natural oil-based fatty acid such as oleic acid may be added in the same manner as described above. Next, an example using a hydroquinone derivative other than the pyrocatechol derivative shown in Example 1 will be briefly described. Example 3 4g epoxy-melamine resin, 1 oleic acid
A conductive paint for screen printing was prepared by mixing 1.5 g of resorcinol, 1.5 g of resorcinol, and 20 g of the above-mentioned Cu powder, and adding an appropriate solvent. A printed resistor was made using the paint according to the same process as in Example 1. The value of specific resistance ρ′ at this time is an average of 1.08Ω/□ (average of 10 pieces)
It was hot. Example 4 4g epoxy-melamine resin, 1 oleic acid
g, phloroglucin 1 g and the Cu powder 20
A conductive paint for screen printing was prepared in the same manner as in Example 1. A printed resistor was made using the paint according to the same process as in Example 1. The average value of ρ' at this time was 7.04Ω/□ (average of 10 samples). Example 5 4 g of epoxy-melamine resin, 1 oleic acid
A conductive paint for screen printing was prepared in the same manner as in Example 1 by mixing 1.5 g of pyrogallol, 1.5 g of pyrogallol, and 20 g of the Cu powder. A printed resistor was made using the paint according to the same process as in Example 1. The average value of ρ' at this time was 2.44Ω/□ (average of 10 pieces). The electrical characteristics of the printed resistors of Examples 3 to 5 are omitted because they are almost the same as those of Example 1. Next, the effects of the present invention will be briefly described. (1) Conductive paints using other metals with low resistivity to replace conventional Ag conductive paints have not been put to practical use. However, by using a paint containing hydroquinone derivatives added to a thermosetting resin,
We were able to provide a Cu conductive paint with a resistivity as low as that of Ag paint. Its specific resistance is
(2) The Cu conductive paint has a sufficiently high heat resistance, which is a low value of 0.02Ω/□. (3) The moisture resistance of the Cu conductive paint can be sufficiently improved by adding a small amount of natural oil-based fatty acids. (4) By using the above paint, powders such as Ni and Cr may also be used in addition to Cu and Ag.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between Cu content f and specific resistance ρ' (Ω/□), Figure 2 is a graph showing the heat resistance characteristics of printed conductors using Cu conductive paint, and Figure 3 is 3 is a graph showing the moisture resistance characteristics of a printed conductor using Cu conductive paint.

Claims (1)

[Claims] 1. A binder made by adding a hydroquinone derivative to a thermosetting resin (hereinafter abbreviated as binder)
A conductive paint using a hydroquinone derivative, which is characterized by dispersing fine metal powder (hereinafter abbreviated as metal powder) as a conductor. 2 The curing temperature of thermosetting resin is at least 110℃
A conductive paint using a hydroquinone derivative according to claim 1, which is characterized by the above characteristics. 3. Any of claims 1 to 2, characterized in that the amount of the hydroquinone derivative added to the thermosetting resin is 30 to 70 parts per 100 parts of pure resin. A conductive paint using the hydroquinone derivative described in item 1. 4 Claims 1 to 3 characterized in that Cu powder is used as the metal powder.
A conductive paint using a hydroquinone derivative according to any one of the items. 5 If the pure resin amount of the thermosetting resin is r, the amount of Cu powder is m, and its content is f, then f=m/r+m×100%, and the value of f is 75% to 85%. A conductive paint using a hydroquinone derivative according to claim 4, characterized in that: 6 Claims 1 to 3 characterized in that Ag powder is used as the metal powder.
A conductive paint using a hydroquinone derivative according to any one of the items. 7. A conductive paint using a hydroquinone derivative according to any one of claims 1 to 3, characterized in that a powder such as Ni, Cr, or Mo is used as the metal powder. 8. A conductive paint using a hydroquinone derivative according to any one of claims 1 to 7, characterized in that an epoxy-melamine resin is used as the thermosetting resin.