JPH04171605A - Conductive paste - Google Patents

Abstract

PURPOSE:To enhance humidity resistance stability to thereby enhance values of practical use by using an inter-graphite-layer compound in which PbCl2 is interposed between graphite layers as a conductive material. CONSTITUTION:At least an inter-graphite-layer compound in which PbCl2 is interposed graphite layers is used as a conductive material. Namely, a metal halogen compound capable of forming a inter-graphite-layer compound through reaction with graphite by itself and PbCl2 are used together, and they are reacted with graphite under a specified synthesizing conditions. Thereby PbCl2 can be inserted so that application to conductive paste of PbC-GIC is made possible. It is thus possible to have conductive paste high values of practical use suitable in forming a resistor and a conductive body excellent in humidity resistance stability, conductivity and characteristics against environment.

Description

[Detailed Description of the Invention] C. Industrial Application Field] The present invention relates to a conductive paste used as a resistance paste for resistors, a conductive paste for conductors, etc. Regarding conductive materials.

[Prior Art] A resistor (resistance pattern) or a conductor (conductive pattern) is generally formed by printing a conductive paste in a pattern shape, drying it, and then thermally curing it. Such a conductive paste is made by kneading an organic binder, a conductive material, a solvent, etc., and the conductivity after curing varies depending on the type of conductive material dispersed in the organic binder.

In other words, conventionally widely known conductive materials for conductive paste include carbon black, graphite, and silver powder, and carbon black is mainly used when forming a high-resistance resistor. However, graphite is mainly used when forming a low resistance resistor.
Further, when forming a conductor with good conductivity, silver powder is mainly used.

However, when forming a resistor with lower resistance than a resistor using graphite as the main conductive material, or when forming a conductor without using expensive materials such as silver powder, it is necessary to use conductive materials that can replace graphite or silver powder. Materials will be needed. In particular, silver-based conductors have the disadvantage of being susceptible to migration in high-temperature and humid environments, so there has been a desire for a conductive material that is highly conductive, environmentally resistant, and inexpensive.

In recent years, graphite intercalation compounds have attracted attention as conductive materials that meet these demands. A graphite intercalation compound is an intercalation compound in which atoms, molecules, ions, etc. are interposed as guests between the layers of graphite as a host, which has a layered crystal structure.It has a low resistivity comparable to that of metals and excellent discharge characteristics. It has high functionality, exhibiting excellent friction properties, low raw material costs, and can be synthesized relatively easily.

Incidentally, a conventional example of a conductive paste containing a graphite intercalation compound as a conductive material includes the one described in JP-A-64-56777.

[Problems to be Solved by the Invention] Although not specifically mentioned in JP-A No. 64-56777, among various graphite intercalation compounds (hereinafter often abbreviated as GIC), FeCQ, etc. C
uCf1. , A Q C8, , NiCM.

Metal chloride-based GICs with such as guests are highly conductive, easy to synthesize, and have a reputation for being relatively stable in the atmosphere. By creating a conductive paste containing the above, it is possible to form a low-resistance resistor or a highly conductive conductor at a low cost, and it is expected to have good environmental resistance.

However, the present inventors discovered that the known metal chloride-based GIC
When an environmental test was conducted under a high humidity atmosphere,
NiCf1. which was considered to be highly stable in the atmosphere.
It was found that -CuCfi and -GIC also showed a large change in resistance value over time.

In addition, when a conductor made by printing a conductive paste containing FeCQ3-GIC dispersed in an organic binder and thermally curing was left in a high humidity atmosphere (40°C, 90% RH), 100 hours elapsed. At this point, the resistance value increased by nearly 30%.

As described above, metal chloride-based GIC, which is expected to be used as a conductive material due to its excellent conductivity, has so far had problems with stability in a high humidity atmosphere, and graphite intercalation compounds have been used as a conductive material. In order to put the conductive paste containing this into practical use, other graphite intercalation compounds, which are inferior in conductivity and ease of manufacture compared to metal chloride-based compounds, must be used, and therefore no significant practical effects have been observed. Ta.

Therefore, an object of the present invention is to provide a conductive paste that uses a metal chloride-based graphite intercalation compound, has improved moisture resistance stability, and has high practical value.

[Means to solve the problem]

The above-mentioned object of the present invention is achieved by using, as the conductive material, at least a graphite intercalation compound in which PBCU is interposed between layers of graphite in a conductive paste in which a conductive material is dispersed in an organic binder. Ru.

[Function] According to experiments conducted by the present inventors, a graphite intercalation compound synthesized using PbCΩ2 and other metal halides (e.g., FeCΩ3 or CuCfi) as guests not only exhibits high conductivity but also exhibits high conductivity. It was confirmed that the stability under a high humidity atmosphere was dramatically improved compared to metal chloride-based GIC. This is due to the characteristics of PbCΩ2 itself: most metal chlorides are deliquescent and easily soluble in water, whereas PbCΩ2 is exceptionally non-deliquescent and poorly soluble in water. be. It is known that metal halides, which are intercalated substances between layers of graphite, have almost the same crystal structure as before insertion, and therefore, even after insertion, the property of being poorly soluble remains unchanged in the case of PBCG. Therefore, as a result of the above, it is considered that GIC into which PbCα2 is inserted has excellent moisture resistance stability.

However, there has been no example of inserting pbcQ between layers of graphite, and it is thought that pbcn alone does not form a graphite intercalation compound under any conditions.

In the present invention, PbCα2 is inserted between graphite layers by allowing pbcn to coexist with a metal halide that can react with graphite alone to form a graphite intercalation compound, and by reacting with graphite under predetermined synthesis conditions. This made it possible for the first time to utilize PbCA, -GIC in a conductive paste.

The process in which PbCΩ2 is inserted between graphite layers is when the halide reacts with graphite.

It is thought that at the same time, it is taken in between the graphite layers. Therefore, the synthesized GIC contains both pbcp and the halides.

If the charging ratio or synthesis temperature of pbcg and other metal halides differs, the moisture resistance stability of the reaction product (graphite intercalation compound) also differs.

According to the results confirmed by the present inventors regarding the conductor using the conductive paste of the present invention, the moisture resistance stability is due to PbCQ occupying in the guest of the graphite intercalation compound.

It was found that it is related to the amount of -For example, guest P
b (1, and FeCQ). As shown in Fig. 5, as the molar ratio of P b / Fe in the insert increases, the resistance stability increases, and the molar ratio of Pb / Fe increases.
If the ratio is 0.05 or more, conventional FeCQ, -GIC
It has better moisture resistance stability than conductors using
If it is above, the moisture resistance stability has improved to a value equivalent to that of a conductor using graphite as a host.

In the present invention, the metal halide used together with PbCl2 has a resin that leads pbcQ between graphite layers, FeCQ, , Cu C(1,, A ff Cg
,,GaCf1. , GoCFl, , M n CQ , ,
CrCQ, MoCQ, Cd(1, etc.) are used, but since FeCR3 and CuCu generate chlorine gas through their own disproportionation reaction, is it necessary to introduce toxic chlorine gas from the outside? The optimum temperature (300 to 55 o'c) at which these react with graphite is preferable because it is industrially advantageous.

When producing the graphite intercalation compound according to the present invention, the ratio of the host to the guest, the charging ratio of PBCG to other metal halides in the guest, and the synthesis conditions are important, and these conditions may differ. The characteristics of the graphite intercalation obtained are also different.

The ratio of P b CQ in the guest of the graphite intercalation compound, which influences the moisture resistance stability of the conductor, is related to both the preparation ratio of the material pbcg and other metal halides and the synthesis temperature, and
The larger the charging ratio with bCα2 and the higher the synthesis temperature, the larger the amount of PB in the generated graphite intercalation compound,
Therefore, moisture resistance stability increases. - As an example, the host is natural graphite with an average particle size of 10 μm, the guest is pbcQ, and Fe
When CQ+ is synthesized in a sealed tube, as shown in the phase diagram of FIG. 6, if the synthesis temperature is 300° C. or higher, FeCQ and a small amount of PbCQ are produced.

If it is inserted between the graphite layers (the area indicated by the broken line in the figure) and the shaded area (area A) in the figure, the moisture resistance stability is equivalent to that of a conductor using host graphite or has no practical problems. It is possible to obtain a conductor that exhibits In addition, in the above-mentioned practically most desirable range, the upper limit of the synthesis temperature is 954°C, which means that the boiling point of pbcu is 954°C.
This is because, if the temperature is higher than that, the pressure inside the reaction vessel will increase significantly, resulting in a dangerous situation. Also, pbcn
The left and right range of the preparation ratio with FeCQ3 is pbcQ.

-95%, FeCQ, -5% to Pb (1, -40%
, FeCQ3-60%. This is F in the mixture
eCl2. If the proportion of PbCα6 is too small, only a very small amount will react with graphite due to the lack of FeCα3 leading PbCα6 to the graphite interlayer, and FeCQ.

The proportion of This is because, in some cases, Fe CQ + preferentially reacts with graphite, and PbCl2 is hardly inserted.

When using another metal halide together with PbCα2, the desired graphite intercalation compound can be obtained by appropriately changing the synthesis conditions.

Therefore, by using the above GIC, a new conductive paste containing a graphite intercalation compound as a conductive material, which has low resistance, which is a characteristic of metal chloride-based materials, and has excellent moisture resistance stability, can be obtained. By printing,
Resistors and conductors with good conductivity and environmental resistance can be formed at low cost.

〔Example〕

Examples of the present invention will be described below based on Table 1 and FIGS. 1 to 6.

Using natural graphite with an average particle size of 10 μm as a host, 9 to 10 − types of PbCf1. -FeCα and -GIC were synthesized. That is, raw material graphite, PbCα2, and FeCα3 are mixed in a Pyrex glass reaction tube at a predetermined charging ratio, heated at 100°C for 1 hour under vacuum suction for sufficient dehydration, and then the reaction tube is melt-sealed. and at a predetermined temperature (300-54
By heating the reaction product at 0'C) for 24 hours and washing the reaction product repeatedly with boiling water and methanol to remove unreacted metal chlorides on the surface, the reaction product shown in Table 1 was obtained.
~9 samples (graphite intercalation compound) were obtained.

Next, the specific resistance of each sample was measured by a four-terminal method in which electricity was applied to the powder sample under pressure and the potential difference of the compressed powder was measured.

The results are also shown in Table 1. In addition, the specific resistance of raw material graphite is 8
．． It was 6mΩ.

As is clear from the table, the larger the PbCΩ2 charge ratio and the higher the synthesis temperature, the higher the ratio of Pb to Fe in the synthesized graphite intercalation compound, which means that PbCΩ2 is inserted between the graphite layers. There is a tendency for it to become easier.

As for the specific resistance, it is observed that the more the weight of the guest relative to the host, the lower it tends to be, and when the weight of the guest is 40% or more, the specific resistance of the host becomes ], / 2 ~
The conductivity was about 1/3, and exhibited high conductivity comparable to that of FeCff and -GIC. The values shown in Table 1 are the specific resistances of the powder compact sample and include the contact resistance between particles, so they are thought to be slightly larger than the specific resistance of the product. It can be done.

Next, each of the samples shown in Table 1 (positive numbers 1 to 9) was treated with an organic binder (phenolic resin) in the presence of a solvent.
After dispersing it into a paste, we printed and heat-cured it to make prototype conductors.
The humidity stability of each sample was evaluated by leaving it at 0° C. and 90% RH and measuring the change in resistance value over time. The results are shown in Figures 1-6. Here, Figure 1 shows the measurement results of a conductor using graphite as a raw material, and Figure 2 shows No.
Measurement results of conductors using samples 1 to 3, Figure 3 shows measurement results of conductors using samples No. 4 to 6, Figure 4 shows results of conductors using Ni samples 7 to 9. The measurement results, Figure 5 shows the Pb/Fe (molar ratio) contained in the GIC of Na 1 to 9 and the evaluation results after 250 hours of humidity resistance, and Figure 6 shows the synthesis conditions (preparation) of No. 1 to 9. and synthesis temperature) are plotted on the phase diagram of the PbCα, -FeCΩ3 system. (In addition, the number above each point in Fig. 6 is the sample number, and the number next to each point is the evaluation result of the resistance value change rate after 250 hours of humidity resistance of each sample.) Also, for comparison, When we prototyped a resistor using a paste in which FeCQ and -GIG were dispersed in the same organic binder and measured the rate of change in resistance of this resistor under the same conditions, we found that the change in resistance over time was saturated even after 100 hours had passed. Without,
The resistance value increased by an average of 27% compared to the starting point.

As is clear from the graphs in Figures 2 to 6, PbCα2-F
A conductor using eCα, -GIC as a conductive material shows little change in resistance value over time in a high humidity atmosphere, especially A in Fig. 6.
GIC synthesized under the synthesis conditions indicated in the area is GIC
Contains Pb in a molar ratio of Pb to Fe of 0.2 or more, and the conductor exhibits excellent moisture resistance stability comparable to that of conductors using graphite as a raw material, or without any practical problems. Ta.

In this way, pbcg and other metal halides are mixed with graphite at a predetermined charging ratio (preferably a molar ratio of PbCα2 equal to or higher than that of other metal chlorides), and this is mixed at a predetermined temperature (preferably 450 molar ratios). When graphite intercalation compounds are synthesized by reacting at temperatures above °C, in addition to the high conductivity that was the advantage of conventional metal chloride-based GICs,
It offers high stability in high humidity atmospheres, which was not possible with
Furthermore, since the raw material cost is low and manufacturing is easy, it can be expected to be used as an excellent conductive material. In other words, a paste in which such a graphite intercalation compound is dispersed as a conductive material is
By appropriately using other conductive materials such as carbon black, it is possible to form low-resistance resistors and conductors with good conductivity that do not change easily even in high-temperature and humid environments at low cost, making it practical. The value is extremely high.

[Effects of the Invention] As explained above, according to the present invention, a graphite intercalation compound which is a metal chloride type but has excellent moisture resistance stability is dispersed as a conductive material, so that it has good conductivity and environmental resistance. It is possible to provide a conductive paste with high practical value and suitable for forming a resistor or conductor with good resistance.

[Brief explanation of the drawing]

All the figures relate to examples of the present invention. Figure 1 is a characteristic diagram showing the humidity stability of raw graphite, and Figure 2 is a synthesis temperature of 300°C.
Figure 3 is a characteristic diagram showing the humidity stability of each sample at a synthesis temperature of 450°C. Figure 4 is a characteristic diagram showing the humidity stability of each sample at a synthesis temperature of 540°C. The characteristic diagram shown in Figure 5 shows the Pb/Fe (molar ratio) contained in the GIC of each sample and their moisture resistance.
FIG. 6 is a diagram showing the evaluation results after 0 hours, and the synthesis conditions for each sample are PbCf1. -FeCQ, is a diagram plotted on the phase diagram of the system. Procedural amendment (voluntary) December 7, 1990

Claims (1)

[Claims] A conductive paste comprising a conductive material dispersed in an organic binder, characterized in that the conductive material is at least a graphite intercalation compound in which PbCl_2 is interposed between layers of graphite.