JPH08222025A - Conductive material - Google Patents

Abstract

PURPOSE: To provide a conductive material with high wear resistance and low electric resistance, used for dipping a contact of a switch. CONSTITUTION: Cylindrically arranged carbon net planes are stacked in the radial direction, first and second graphite fine fibers having different diameters are mixed to a resin binder. The first graphite fine fibers have a diameter D1 of 0.3μm to 10μm and a length L of 5μm to 100μm, and the second graphite fine fibers have a diameter D1 of 50Å to 200Å and a length L of 1μm to 30μm. It is preferable to add carbon black to the graphite. The conductive material obtained has a low volume resistivity value and high wear resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive material (conductive composition) used as a contact of a leaf switch or a resistor layer of a variable resistor. The present invention relates to a conductive material (conductive composition) capable of increasing the resistance and decreasing the volume resistance value.

[0002]

2. Description of the Related Art A conductive material containing a carbon material is used as a contact of a switch or a resistor layer of a variable resistor.
A conductive material containing a carbon material does not have the problem of oxidation or sulfidation unlike a material using a precious metal powder such as gold or silver, and can be manufactured at a lower cost than a material using a precious metal powder.

As this kind of conductive material, there is a material in which carbon black (fine carbon powder) is mixed in a thermosetting resin such as a phenol resin. However, a conductive material containing only carbon black has a high electric resistance value and is inferior in wear resistance. Therefore, a resin binder in which carbon black and a minute piece of plate-like graphite having a crystal layer laminated thereon are mixed is generally used.

[0004]

The conductive material in which the carbon black and the minute pieces of plate-like graphite are mixed has an initial resistance value lower than that in which the carbon black alone is mixed. However, if, for example, the contact of the switch is coated with the above conductive material and the contact of the contact is repeated, the conduction resistance increases as the number of contact of the contact increases.

FIG. 5 shows a leaf switch in which a conductive material in which carbon black and minute pieces of plate-like graphite are mixed is applied to the contacts, and the number of times the contacts are repeated and the conduction resistance between the contacts. It shows the relationship with change. In FIG. 5, the horizontal axis represents the number of times the leaf switch contacts are repeated, and the vertical axis represents the conduction resistance (Ω) between the contacts. That is, contact of the contact of the leaf switch 0 times,
Conduction resistance between contacts was measured for each leaf switch that was repeated 10,000 times, 30,000 times, and 50,000 times, and the average of the measured values of the conduction resistance at each contact number was "○".
It is plotted with a mark.

FIG. 5 reveals that the conduction resistance between the contacts increases as the number of contacts of the contacts increases. This is because the conductive material mixed with carbon black and minute particles of plate-like graphite can lower the initial resistance value, but cannot improve the wear resistance or the mechanical strength so much that the contact of the contact It is predicted that the resin binder, carbon black, and plate graphite will be abraded by mechanical impact or friction due to the, and the abraded powder will adhere to the contacts and further solidify to form a high-resistance third body. To be done.

In addition, regarding the resistance value of the contact of the switch,
When a current is simply passed between contacts to detect ON and OFF, the increase in resistance of the conductive material does not pose a problem. However, recently, multiple sets of switches and resistors connected in series were connected in parallel, and by detecting the current flowing in the circuit, etc., it was determined which contact of the switch corresponding to which resistor was closed. There is something to detect.
In such usage of the switch, if the conduction resistance of the contact of the switch increases, accurate switch detection cannot be performed. Therefore, a conductive material having an increased conduction resistance as shown in FIG. 5 cannot be used for this type of switch.

Further, as a conductive material having high mechanical strength, there is a resin binder in which thick carbon fibers having a diameter of about 80 μm are cut and mixed into several hundreds of μm.
In this conductive material, the abrasion resistance can be improved to some extent by incorporating carbon fibers. However, since thick and short carbon fibers are mixed in the resin binder, the contact state between the carbons in the resin binder is not flexible, and therefore the volume resistance value is relatively high. In addition, this conductive material is unlikely to be ink-like or paste-like in the state of the mixture before curing, and is inferior in ductility, so that a conductor layer or a resistor layer is formed by pattern formation or printing. Will be difficult to do. Also, since it does not become a paste, it is difficult to dip it to the contact of the switch.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a conductive material which can realize a low volume resistance value and high mechanical strength such as abrasion resistance.

[0010]

The conductive material of the present invention comprises:
In the resin binder, carbon mesh planes arranged in a cylindrical shape are laminated in the radial direction of the cylinder, and first and second fine graphite fibers having different diameters are mixed.

In the above description, what is mixed in the resin binder is a first graphite fine fiber having a diameter of 0.3 μm or more and 1.0 μm or less and a second graphite fine particle having a diameter of 50 Å or more and 200 Å or less. It is a fine fiber.

In the above, it is preferable that carbon black (fine carbon powder) is added to the resin binder together with the first and second fine graphite fibers.

When the first and second graphite fine fibers have a combination of the above diameters, the second graphite fine fiber is 0.3 g or more and 1.0 g or less with respect to 1 g of the first graphite fine fiber. It is preferable that the first graphite fine fibers are mixed in a ratio of 10% by volume or more and 50% by volume or less.

When carbon black is added to the first and second graphite fine fibers, 0.2 g of carbon black is added to 1 g of the first graphite fine fiber.
It is preferable that the amount is g or more and 0.3 g or less.
In this case, a ratio of the second graphite fine fibers of 0.3 g or more and 0.4 g or less is preferable.

In the conductive material (conductive composition) of the present invention, first and second fine graphite fibers in which carbon mesh planes arranged in a cylindrical shape are laminated in the radial direction of the cylinder are used. The first and second graphite fine fibers are
The benzene rings are continuously connected in a net-like fashion in a circular shape.

FIG. 1 is a perspective view for explaining the crystal structure of the first and second graphite fine fibers. This graphite fine fiber is a vapor-grown carbon fiber, and is a vapor-grown carbon fiber centered on ultrafine particles suspended in hydrocarbon vapor. As shown in FIG. 1, the crystal structure of graphite fine fibers is a graphite structure in which hexagonal mesh planes of carbon are arranged in a cylindrical shape and arranged, and layers in which hexagonal mesh planes are connected are laminated in the radial direction of the cylinder. . In addition, a hollow core is formed at the center of the fiber.

The first graphite fine fibers used in the conductive material of the present invention are conventional carbon fibers (diameter 80).
The diameter is D1
Is 0.3 μm or more and 1.0 μm or less. Also length L
Is 5 μm or more and 100 μm or less. Therefore, the aspect ratio (ratio of the diameter D1 and the length L) is 1:50 to 1:33.
3.3. Also, the second graphite fine fibers are even narrower than the first graphite fibers,
The diameter D1 is 50 angstroms or more and 200 angstroms or less. The length L is 1μm or more and 30μ
m or less and the aspect ratio is 1:50 to 1: 600
0. That is, as the first and second graphite fine fibers used in the conductive material of the present invention, long and narrow aspect ratios of 1:50 or more are used.

Comparing the conventionally used carbon fiber with the above graphite fine fiber, the diameter of the conventional carbon fiber is about 80 μm, and the diameter of the first graphite fine fiber is 1/80 or less of that of the carbon fiber. , Second
The diameter of graphite fine fiber is 1/4 that of carbon fiber
It is 000 or less. Further, when the conventional carbon fiber is mixed into the conductive material, the aspect ratio is about 1:10 or less, which is thick and short, whereas the first and the second used for the conductive material of the present invention. The aspect ratio of the graphite fine fibers is 1:50 or more as described above, and is extremely elongated.

The first and second fine graphite fibers are elongated and slender as compared with conventional carbon fibers, and the hexagonal mesh planes are continuously connected in a cylindrical shape, so that they are unlikely to break or tear and have mechanical strength. It is expensive. It also has excellent wear resistance. Further, the elongated first and second fine graphite fibers are highly flexible as a whole and have good dispersibility in the resin binder. Further, the first and second graphite resins are surface-treated with an inert gas, and if necessary, the graphite fine fibers mixed in the resin binder are preliminarily dispersed by ultrasonic waves and then kneaded. In this case, the dispersion rate of the graphite fine fibers becomes high, and it becomes possible to manufacture a conductive material having a uniform electric resistance value at each site.

As described above, the first graphite fine fibers have a diameter D1 of 0.3 μm to 1.0 μm, are finer than conventional carbon fibers, have a large aspect ratio, are highly flexible, and have a crystal structure. Therefore, it has excellent mechanical strength such as abrasion resistance. Therefore, it is possible to reduce the volume resistance value of the conductive material in which only the first graphite fine fibers are mixed in the resin binder, as compared with the conventional conductive material in which carbon fibers having a diameter of about 80 μm are mixed. .

However, in a conductive material in which only the first graphite fine fibers are mixed in the resin binder, the diameter of the first graphite fine fibers is still large,
The resin binder remains between the first graphite fine fibers, and a portion having a coarse graphite fine fiber density is generated.
There is a limit in reducing the volume resistance value. In addition, when only the first graphite fine fibers are mixed, the graphite fine fibers are likely to have a coarse / dense structure in the resin binder, the mechanical strength is lowered in the coarse region, and the resin binder is likely to peel or crack. Will be things. On the other hand, a conductive material in which only a second fine graphite fiber having a smaller diameter is mixed in a resin binder is also conceivable. However, since the second fine graphite fiber is used as a very long one having a large aspect ratio, this alone is used. Then, the dispersibility in the resin binder deteriorates.

Therefore, in the present invention, both the first and second fine graphite fibers are mixed in the resin binder. By mixing the first graphite fine fibers with the finer second graphite fine fibers, the coarse second graphite fine fibers are filled with the fine second graphite fine fibers, resulting in volume resistance. The value is very small. Further, by mixing two kinds of graphite fine fibers having different thicknesses, the fine graphite fibers do not become coarse and dense, and the mechanical strength increases. Furthermore, by entwining the thick second graphite fine fibers with the thin second graphite fine fibers, the dispersibility of the graphite fine fibers in the resin binder is improved, and the mixture before curing becomes a paste or ink. It will be easier.
Therefore, it is possible to easily perform a dip on the contact of the switch or a pattern film formation on the substrate of the variable resistor.

When carbon black is further mixed into the first graphite fine fiber and the second graphite fine fiber, the density of the carbon material in the resin binder is further reduced, the volume resistance value is further reduced, and Friction is also improved.

Next, as the resin binder, a thermosetting resin such as a phenol resin, an epoxy resin, a fluorine resin, or an acrylic resin is preferably used, and polypropylene, polyethylene, polyphenylene sulfide, polyethyl ketone is used. It may be a thermoplastic resin such as. Further, as the solvent, methyl ethyl ketone or a substitute thereof is used, or acetone, ethanol, methanol, an ether solvent or the like is used.

When the resin binder is a thermosetting resin, the kneaded mixture is dipped on the contacts of the switch, or patterned into a predetermined shape as a resistor layer or a conductor layer, and then baked and cured. To be When the resin binder is a thermoplastic resin, it is injection-molded into a shield case or switch contact shape, and is cooled and cured.

[0026]

【Example】

(Example 1) The diameter is 0.3 μm or more and 1.0 μm or less,
First graphite fine fibers having a length of 5 μm or more and 100 μm or less, and a diameter of 50 Å or more and 200 Å or less, and a length of 1 μm or more and 30
A second graphite fine fiber having a particle size of not more than μm was mixed with a solvent into a phenolic binder resin, and the mixture was kneaded with a three-roll mill to form a paste, which was further baked at 180 ° C. for 40 minutes. The ratio of both graphite fine fibers was 0.3 g of the second graphite fine fiber to 1 g of the first graphite fine fiber. That is, the weight ratio of the second graphite fine fiber to the first graphite fine fiber was 0.3.

(Example 2) A fired product similar to that of Example 1 was used, in which the second graphite was added to the first graphite fine fiber (1 g).
The graphite fine fiber of No. 1 was set to a ratio of 0.6 g. That is, the weight ratio of the second graphite fine fibers to 1 of the first graphite fine fibers was set to 0.6.

(Example 3) A fired product similar to that of Example 1, except that the ratio of 1 g of the second graphite fine fiber to 1 g of the first graphite fine fiber was used.

COMPARATIVE EXAMPLE 1 Only the first graphite fine fibers were mixed with a solvent in a phenolic resin binder, kneaded with a three-roll to form a paste, and fired.

In each of Examples 1 to 3 and Comparative Example 1, the volume fraction (volume%) of the first graphite fine fiber in the solid was changed stepwise, and the volume was produced. The resistance value (Ω · cm) was measured. The result is shown in FIG. In FIG. 3, “×” is the measurement result of Example 1, “□” is the measurement result of Example 2, “Δ” is the measurement result of Example 3, and “◯” is the measurement result of Comparative Example 1. Further, the horizontal axis is the volume fraction (volume%) of the first graphite fine fiber, and the vertical axis is the measured value of the volume resistance value (Ω · cm).

In the measurement results of FIG. 3, the volume resistance values of the conductive materials of Example 1, Example 2 and Example 3 are
Comparative Example 1 in which only the first graphite fine fibers were mixed
It can be seen that it is significantly lower than Therefore, as the conductive material of the present invention, 0.3 g of the second graphite fine fiber is used for 1 g of the first graphite fine fiber.
As described above, it is preferable that they are mixed in a ratio of 1.0 g or less. Further, when the ratio of the second graphite fine fiber to 0.1 g of the first graphite fine fiber is 0.1 g or more, it is 1.
If it is 0 g or less, the volume resistance value can be reduced as compared with Comparative Example 1. Therefore, the preferable ratio of the second graphite fine fiber to the first graphite fine fiber 1 g is 0.1 g or more, or 0.1 g or more and 1.0 g or more.
It is the following, and more preferably 0.3 g or more and 1.0 g
It is the following.

Further, it can be seen from FIG. 3 that the volume resistance value is affected when the volume fraction of the first graphite fine fiber changes in each of Example 1, Example 2 and Example 3. From FIG. 3, Example 1, Example 2, Example 3
In each of the above, in order to make the volume resistance value around 10 −1 (minus square) or less, it is preferable that the volume fraction of the first graphite fine fiber is 10% by volume or more and 50% by volume or less, Furthermore, this is preferably 10% by volume
It is 40 volume% or less above.

Next, the test results of the contact life when the conductive material of the present invention is applied to the contact of the leaf switch will be described.

(Example 4) The first graphite fine fiber and the second graphite fine fiber were mixed with a solvent in a phenolic resin binder, and the mixture was kneaded by a three-roll mill. The leaf switch shown in FIG. Contacts 2 and 3 of 1
It was dipped in the portion indicated by C at the tip of the above and baked at 180 ° C. for 40 minutes. The weight ratio of the first and second graphite fine fibers was set to 0.6 g of the second graphite fine fiber to 1 g of the first graphite fine fiber. Further, the volume fraction of the first graphite fine fibers in the solid of the fired conductive material was set to 30% by volume.

(Embodiment 5) The first graphite fine fiber, the second graphite fine fiber, and further carbon black were mixed with a solvent in a phenol resin binder and kneaded with a three-roll mill to prepare a leaf switch 1. Dip the contact points 2 and 3 at the tip of C, 180 ℃
It was baked for 40 minutes. The weight ratio of the first and second graphite fine fibers to carbon black was 0.4 g of the second graphite fine fibers and 0.2 g of the carbon black with respect to 1 g of the first graphite fine fibers. Further, the volume ratio of the first graphite fine fibers during fixing of the fired conductive material was set to 30% by volume.

(Embodiment 6) With the same composition as in Embodiment 5, the weight ratio of the first and second graphite fine fibers to the carbon black was changed to 1 g of the first graphite fine fibers and the second graphite fine fibers. Fiber was 0.3 g and carbon black was 0.3 g. The volume ratio of the fired conductive material first graphite fine fibers was set to 30% by volume.

(Comparative Example 2) The first graphite fine fibers and carbon black were mixed with a solvent in a phenolic resin binder, and the mixture was kneaded by a three-roll mill. The contact 2 of the leaf switch 1 shown in FIG. And C at the tip of 3
Was dipped in the part indicated by and baked at 180 ° C. for 40 minutes. The weight ratio of the first graphite fine fibers to carbon black was 0.6 g of carbon black with respect to 1 g of the first graphite fine fibers. In addition, the volume fraction of the first graphite fine fibers of the fired conductive material is set to 30.
The volume% was defined.

The above-mentioned fourth, fifth and sixth embodiments,
The result of the contact test of the contacts 2 and 3 of each leaf switch of Comparative Example 2 is shown in FIG. The horizontal axis of FIG. 4 represents the number of contacts between the contacts 2 and 3, and the vertical axis represents the change in the conduction resistance value (Ω) between the contacts 2 and 3 of the leaf switch 1.
In FIG. 4, the mark “◯” is the example 4, the mark “Δ” is the example 5, the mark “x” is the example 6, and the mark “□” is the comparative example 2.
That is, the contact between the contact points 2 and 3 of the leaf switch is 0 times,
Conduction resistance between the contacts was measured for each leaf switch 1 that was repeated 10,000 times, 30,000 times, and 50,000 times, and the average of the measured values of the conduction resistance at each contact number was plotted with "○" to "□" marks. Is.

As a result of the contact test shown in FIG. 4, in the leaf switch of Comparative Example 2, the contact resistance value increases as the number of times of contact is repeated. On the other hand, Example 4, Example 5, and Example 6
Then, it can be seen that the contact resistance value hardly changes even if the number of contacts increases. Further, the fifth embodiment is more preferable than the fourth embodiment.
It can be seen that, in Example 6, the increase in conduction resistance is small even if the number of contacts increases.

That is, in Comparative Example 2 in which the first graphite fine fibers and carbon black were mixed in the resin binder, in Example 4 in which both the first and second graphite fine fibers were mixed, the contact of the contact point was made. It can be seen that the increase in the resistance value due to the above is small, and that in the case where the carbon black is added together with the first and second fine graphite fibers, the increase in the resistance value due to the contact of the contacts is further reduced.

In each of the embodiments, the mechanical strength reduction due to the contact between the contacts 2 and 3 is small, and a high resistance third body in which carbon powder or the like is solidified is formed on the surface of the conductive material of the contacts 2 and 3. It means that it is hard to be done, and the conductive material in which carbon black is further mixed in the first and second graphite fine fibers has higher mechanical strength.

Further, from the results of FIG. 4, when the first and second graphite fine fibers and carbon black are mixed, the second graphite fine fiber is added to the first graphite fine fiber 1 g. 0 for 0.3 g or more,
It is preferable that the weight ratio is 4 g or less and the carbon black is 0.2 g or more and 0.3 g or less. The ratio of carbon black to 0.1 g of graphite is 0.1.
If it is g or more and 0.8 g or less, it is possible to reduce the decrease in conduction resistance due to repeated contact of the contacts, as compared with Comparative Example 2. Therefore, in the conductive material in which carbon black is mixed in the first and second graphite fine fibers, the ratio of carbon black is 0.1 g or more and 0.8 g or less with respect to 1 g of the first graphite fine fiber. It is preferable.

The conductive material in each of the above embodiments has a small initial resistance value as shown in FIG. 3 and does not increase in resistance value even if contact is repeated as shown in FIG. Therefore, a circuit in which a switch and a resistor are connected in series is connected in parallel and a circuit that detects the current flowing in the circuit and detects which resistor corresponds to which switch has the contact closed When used for, the conduction resistance of the switch is reduced, and highly accurate detection is possible.

[0044]

As described above, according to the present invention, as a conductive material used as a switch contact, a conductor layer or a resistor layer, mechanical properties such as abrasion resistance are excellent and a volume resistance value is uniform. And low resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a crystal structure of graphite fine fiber,

FIG. 2 is a perspective view showing a leaf switch in which a conductive material of the present invention is dipped in a contact.

FIG. 3 is a diagram showing the relationship between the volume fraction and the volume fraction of the first graphite fine fiber in Examples 1 to 3 of the present invention and Comparative Example 1.

FIG. 4 is a graph showing the relationship between the contact resistance and the contact resistance of leaf switches using the conductive materials of Examples 4 to 6 of the present invention and Comparative Example 2;

FIG. 5 is a diagram showing the relationship between the contact resistance and the contact resistance of a leaf switch in which a conventional conductive material is dipped in the contact;

[Explanation of symbols]

 1 Leaf switch 2 and 3 contacts

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motonobu Takeya 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (72) Inventor Takehiro Takojima 1-7 Yukiya-Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (72) Inventor Yoshikazu Kakihara 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd.

Claims (6)

[Claims] 1. A first graphite fine fiber in which carbon mesh planes arranged in a cylindrical shape are laminated in a radial direction of the cylinder,
Similarly, carbon mesh planes arranged in a cylindrical shape are laminated in the radial direction of the cylinder, and a second graphite fine fiber having a diameter smaller than that of the first graphite fine fiber is mixed in the resin binder. Conductive material characterized by. 2. The conductive material according to claim 1, wherein the diameter of the first graphite fine fibers is 0.3 μm or more and 1.0 μm or less, and the diameter of the second graphite fine fibers is 50 angstroms or more and 200 angstroms or less. . 3. The conductive material according to claim 1, wherein carbon black (fine carbon powder) is added in the resin binder. 4. The first graphite fine fiber is 1 g, and the second graphite fine fiber is 0.3 g or more.
The conductive material according to claim 2 or 3, which is mixed in a ratio of 0 g or less. 5. The conductive material according to claim 4, wherein the volume fraction of the first graphite fine fibers is 10% by volume or more and 50% by volume or less. 6. The conductive material according to claim 3, wherein carbon black is mixed in an amount of 0.2 g or more and 0.3 g or less with respect to 1 g of the first graphite fine fibers.