JPH03137011A - Improved graphite powder, dry cell and sliding member - Google Patents

Abstract

PURPOSE:To improve specific surface area, electric resistivity, etc., of graphite by pulverizing graphite with shearing force parallel to the plane of carbon net in the grain with using a roll mill, etc. CONSTITUTION:Graphite is improved by pulverizing with shearing force parallel to the plane of carbon net in the graphite grain. A dry cell containing this improved graphite can be easily produced and has excellent properties such as long life. A sliding part containing this graphite has enough lubricating property and wear resistance, etc. The source material for the improved graphite is preferably an artificial graphite containing little heavy metal. Graphite is pulverized mostly with shearing force parallel to the plane of carbon net in the graphite grain, and pulverization to give such shearing force to the grains can be performed with not only a roll mill but a ball mill, especially vibrating ball mill, or stamp mill, and preferably disk vibrating mill, and more preferably roll mill. An ang mill is extremely preferably since it pulverizes with only shearing force in principle. However, a roll mill is most preferable from the viewpoint of workability and productivity.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an improved graphite powder, a dry battery, and a sliding member, and more specifically, a conductive material for a dry battery, a sliding member,
Graphite powder with a large specific surface area, excellent formability, high liquid retention rate, and low lubricity, used as a raw material for producing pencil lead or silicon carbide, etc., and dry batteries and sliding devices containing the graphite powder. This relates to members.

(Prior Art) Graphite powder has various aspects such as specific surface area, electrical resistivity, crystallite size, etc., and has various uses depending on its properties.

For example, in recent years, the production of non-aqueous electrolyte batteries, commonly known as dry batteries, has shown remarkable growth. The positive electrode mix plays an extremely important role, and depending on the type of battery, manganese dioxide, silver oxide, silver chloride, etc. are used as active materials in this positive electrode mix, which control electronic conduction. Carbonaceous powder is used as the conductive material in most dry batteries.

However, while these various dry batteries have excellent continuous discharge performance, high load discharge performance, and storage stability, they are also required to be easily manufactured from stable and easily available raw materials. Good formability, (
2) Large specific surface area, (3) Desired particle size, (4) Good adhesion to the active material, (5) High reactivity with the electrolyte, (6) Impurities and (7) high performance in retaining a large amount of electrolyte.

Specifically, as a conductive material, acetylene blank, which has an excellent electrolyte retention rate, is mainly used for manganese dry batteries, and for alkaline manganese dry batteries, lithium dry batteries, etc., it is easily formed into cylindrical or disc shapes. Natural flaky graphite powder, which easily retains its shape, has been mainly used.

In addition, graphite can be used as a composite material using copper-based iron-based metals, amorphous carbon, or various resins as a binder, such as bearing materials, sealing materials, gasket materials, flage materials, sliding materials for panda graphs, and trolley materials. Used in mechanical and electrical sliding members such as wheels. The properties of graphite required for these sliding parts include lubricity, wear resistance, load resistance,
Mechanical strength, thermal expansion, chemical stability, etc. are important, and lubricity is particularly important. However, the artificial graphite powder that has been mainly used in the past has a high coefficient of friction, which is an indicator of lubricity, and therefore, for example, when the content of graphite powder is increased to improve strength, the lubricity decreases. are doing.

Graphite is also used as a filler material in various plastics such as phenol, epoxy, and tetrafluoroethylene to improve the load carrying capacity and wear resistance of the plastics. However, when conventional artificial graphite powder is used, there are still problems such as a large decrease in tensile strength and elongation.

Furthermore, most of the graphite powder used as raw material for pencil lead is natural flaky graphite powder because lubricity is required during writing, and the graphite powder used in silicon carbide production has a more active reaction In order to achieve this, a powder with an extremely large surface area per unit weight is used.

(Problems to be Solved by the Invention) As mentioned above, acetylene black, natural flaky graphite, and artificial graphite are examples of carbonaceous materials used for various purposes, but all of them have sufficient properties required for each purpose. It does not reach the point where it has a satisfying quality.

For example, regarding the physical properties of acetylene black, JIS
K-1469, and its first feature is that it has a large amount of hydrochloric acid absorption, which indicates electrolyte retention performance, but its formability is inferior to any other conductive material. In addition, natural graphite powder has excellent shapeability because its graphite crystals are more developed and flat, but it is difficult to say that it can always be obtained stably at a low price since it is completely dependent on imports. Furthermore, when aiming at high-performance dry batteries, there is a problem in that it is difficult to remove impurities existing between graphite crystal layers.

On the other hand, artificial carbonaceous powder is easily available as a powder of stable quality, and its most distinctive feature is that it contains extremely low impurities, making it possible to easily obtain a powder with a desired particle size range, but it also requires lubrication. There were difficulties in properties, hydrochloric acid absorption, formability, etc.

As a result of intensive studies to solve this problem, the inventors of the present invention found that the surface area per unit weight ( Specific surface area (hereinafter referred to as specific surface area) increases dramatically, shapeability, crushing strength after shaping (referred to as cohesive force) and liquid retention rate increase, lubricity improves, electrical resistance decreases, etc. We discovered that the physical properties changed completely and arrived at the present invention.

That is, the object of the present invention is to provide graphite powder that exhibits properties equivalent to or superior to natural flaky graphite in terms of electrical resistance, specific surface area, formability, cohesive force, liquid retention, lubricity, etc., as well as continuous discharge performance,
It is an object of the present invention to provide a dry battery with excellent high-load discharge performance, storage stability, etc., and a sliding member with excellent lubricity and anti-yielding properties, which are industrially advantageous.

(Means for Solving the Problems) Therefore, the object of the present invention is to provide an improved graphite powder obtained by pulverizing graphite mainly by shearing force parallel to the plane of the carbon network of the graphite, and a conductive material using the improved graphite powder. This can be easily achieved by using a dry battery containing the improved graphite powder and a sliding member containing the improved graphite powder.

(effect) The present invention will be explained in detail below.

The improved graphite powder of the present invention is produced by crushing graphite while applying a shearing force mainly parallel to the carbon network plane of the graphite crystallites, and the dry cell and sliding member of the present invention are characterized by: It is characterized by containing the improved graphite powder produced as described above as a conductive material or a lubricant.

Graphite is a plate-shaped crystal formed by aggregation of microcrystals formed by stacking carbon network planes with their directions aligned with each other, and the directions of the plate planes of the plate-shaped crystals and the carbon network planes coincide with each other.

Therefore, for example, when graphite is crushed using a roll mill, the graphite is inevitably rolled into the gap between the rolls so that the plane of the carbon network coincides with the tangential plane of the circumferential surface of the roll. If there is a difference in speed, a strong shearing force parallel to the plane of the carbon network is applied.

Other pulverization methods in which a strong shearing force parallel to the plane of the carbon network is applied and pulverization is performed mainly by the contribution of the shearing force include ball mills, especially vibrating ball mills, stamp mills,
More preferred is a disk vibrating mill, and even more preferred is a rod mill.Although an ong mill is a device that performs pulverization using only shearing force in principle and is very preferred, Considering this, a roll mill is the most preferable crushing device for use in the present invention.

When using a roll mill, the larger the difference in peripheral speed between the two rolls that crush the graphite, the greater the shearing force, which results in a larger specific surface area of the resulting improved graphite powder and a lower electrical resistance. It is appropriate that the ratio of the circumferential speeds is 1:1.2 or more, more preferably 1:2 or more, and most preferably 1:3 or more.

However, graphite is not always rolled into the roll at an angle such that the tangential plane of the roll circumferential surface and the plane of the carbon network perfectly match, so even if there is no difference in the circumferential speed of the two rolls, the carbon network A strong shearing force parallel to the plane is applied, and in this case, the shearing force contributes more to the crushing than the pressure of the rolls, and a significant effect is seen in terms of improving the specific surface area and electrical resistance characteristics.

In any case where the carbonaceous powder is used, it is preferable that there are fewer impurities mixed therein. In the case of dry cell batteries, the presence of impurities causes polarization and self-discharge, resulting in short battery life. In addition, when used as a raw material for pencil lead, the lubricity is impaired especially if metal is mixed in, and when producing silicon carbide, the production of silicon carbide is inhibited. Especially for dry batteries, Cu,
Heavy metals such as Ni, Co, Fe, Sb, As, Mo, and V pose a problem. The following table shows an example of the analysis results of various carbonaceous powders.

C unit: ppm) The graphite used as a raw material in the present invention may be either natural or artificial, but for the above reasons, it is preferable to use artificial graphite.

In addition, the crushing device used in the present invention is preferably designed to avoid metals from being mixed into the graphite. For example, in the case of a roll mill, ordinary steel rolls may be used, but as mentioned above, in particular In the case of graphite powder for conductive materials for batteries or raw materials for pencil leads, it is undesirable if metal is mixed in, so use a chrome-plated steel roll, more preferably a stainless steel roll, and even more preferably a chilled layer on the surface by quenching. It is preferable to use a steel roll, most preferably a ceramic roll, to prevent metal contamination.

Considering formability, liquid holding rate, lubricity, etc., the improved graphite powder produced by the present invention has a specific surface area of 50 m 7 g or more, preferably 80 m 7 g or more, and a liquid holding rate of 15 mffi.
15g or more, more preferably 18ml/5g
As mentioned above, the friction coefficient (this polymorphism) as an index indicating lubricity is 0.24 or less, preferably 0°22 or less, and the crystallite size Lc, which is one index of graphite crystal, is more preferably B than 1000 Å. .

It is appropriate to manufacture the film so that the thickness is 0 Å or less.

Furthermore, in the case of the present invention, it is possible to use a dry method in which nothing is added to the graphite, a very small amount of one or more types of dispersants or surfactants added in combination, or a wet method. be. By adding a dispersant or the like together with graphite as a raw material, a new fracture surface is generated and, at the same time, the dispersant or the like is fixed on the surface of the graphite by a mechanochemical phenomenon, which is extremely advantageous because wettability can be improved.

When a shearing force parallel to the carbon network plane of graphite is applied, the specific surface area increases dramatically, the liquid retention rate increases, and Lc decreases.
Although the exact reason for the improved lubricity is not clear,
As the grinding time increases, the overall blackness in X-ray diffraction gradually increases, but the diffraction lines do not spread significantly and appear sharply, so the size of individual crystallites does not decrease and becomes tertiary. It is understood that amorphousization occurs due to original refinement.

Considering more specifically, when a shearing force parallel to the plane of the carbon network is applied, the carbon crystallites move between the walls along the plane of the carbon network, and at the same time distortion occurs in the crystal, so that the lattice constant Co of the crystal changes.
It was confirmed by X-ray diffraction that the crystallite size Lc decreased.

Therefore, the true specific gravity decreases and the particle size decreases, resulting in a significant increase in the specific surface area and liquid retention rate. However, since the size of the individual crystallites does not decrease, it is thought that the lubricity improves.

Various dry batteries can be obtained by conventional methods using the improved graphite powder of the present invention as a conductive material. That is, manganese dry batteries,
Alkaline manganese dry batteries, silver oxide dry batteries, lithium dry batteries, etc. can obtain various improvements in performance as described below.

First, when the improved graphite powder of the present invention is used as a conductive material for the positive electrode mixture of dry batteries, for example, when 1/2 of acetylene black is replaced, the electrical resistivity changes from 0.26Ω・ClTl to 0 according to JISK-1469. The conductivity is reduced to 0.08 Ω·cm, and the conductivity can be significantly improved. Furthermore, since the improved graphite powder of the present invention has a high specific surface area, an electrolyte retention capacity comparable to that of an acetylene blank can be obtained, and since the packing density is high, the volume ratio occupied by the conductive material can be reduced to 80 or less compared to 100 for the conventional graphite powder. This makes it possible to significantly increase the filling amount of the positive electrode active material.

In addition, in this type of battery, during high-temperature storage, a small amount of water in the positive electrode mixture evaporates, causing the upper part of the molded positive electrode mixture to shrink, creating a void between the mixture and the separator, which prevents discharge. Although the reaction area may be reduced, this occurrence can be reduced by using the improved graphite powder of the present invention.

Further, the improved graphite powder of the present invention can be used to create a composite material with amorphous carbon, resin, or metal by a conventional method, and can be used as a mechanical or electrical sliding member. Examples of mechanical sliding members include bearing materials, sealing materials, hones, gaskets as fixed sealing materials, and the like, while electrical sliding members include brush materials, pantograph sliders, trolley wheels, and the like. The sliding member of the present invention has sufficiently improved properties such as lubrication, mold release, wear, and friction. It can also be used as a seal material or as a bell bearing in places where lubrication is not possible.

(Examples) The present invention will be explained in more detail by Examples below, but the present invention is not limited by the Examples unless it exceeds the gist thereof.

Example 1 Electrical resistivity was measured for improved graphite powders A and B and other samples obtained by crushing highly graphitized coal-based artificial graphite powder in a roll mill 10 times or 5 times, respectively, and the results are shown in Table 1. The results shown in Table 2 were also obtained by measuring the electrical resistivity of the improved graphite powder A, acetylene black, and a carbonaceous powder obtained by mixing the two. In addition, all measurements of electrical resistivity were performed based on the test method of JIS K-1469.

It is extremely low, and is effective not only when used alone but also when used in combination with acetylene black.

Example 2 Various physical properties were measured for graphite powder and other carbonaceous powder obtained by crushing highly graphitized coal-based artificial graphite powder 0 to 10 times in a roll mill, and the results shown in Table 3 were obtained. .

In this example, a powerful three-roll mill was used.

The roll mill used in Examples 1 and 2 had a diameter of 1
A powerful 3-roll mill consisting of 3 6-inch chilled cast iron rolls, each with a rotation speed of 100.
times/min (peripheral speed 127 m/min), 300 times/min, and 900 times/min.

As shown in Tables 1 and 2, the improved graphite powder produced according to the present invention has the electrical resistivity required for a conductive material in Example 3.
Fill a cylindrical container with a height of 200 mm, and pour 3 to
After molding with a load of n, the load was removed and a disc-shaped molded product was taken out. At this time, the thickness H of the carbonaceous powder when a load was applied and the thickness l of the carbonaceous powder after the load was removed were measured.

Subsequently, a force was applied perpendicularly to the formed disk from the side, the force P required to break the disk was measured, and 2P/πdl was calculated as an index of cohesive force. In addition, the specific gravity of the disk was also measured. The results are shown in Table 4.

Example 4 As an electrical sliding member, a graphite powder obtained by crushing the artificial graphite powder used in Example 1 by passing it through a roll mill 15 times, or a mixture of 80 parts of conventional artificial graphite powder and 20 parts of phenol resin was used. The physical properties of the product manufactured by molding and heat treatment at 1000 degrees were measured, and the results shown in Table 5 were obtained.

Table 5 As shown in Table 5, when the improved graphite powder produced according to the present invention is used, the bulk specific gravity and bending strength are improved compared to the conventional artificial graphite powder, the specific resistivity is significantly lowered, and the electric sliding It shows extremely good physical properties as a moving member.

Example 5 A machine sliding member was manufactured by blending the same improved graphite powder as used in Example 4 with tetraethylene ethylene resin (PTFE) at a different content ratio, and its physical properties were measured. death,
The results shown in Table 6 were obtained.

As shown in Table 6, when improved graphite powder is used, all physical properties such as tensile strength, elongation, compressive strength, bending strength, friction coefficient, and wear rate improve, making it suitable for mechanical sliding parts. Shows good properties.

(Effects of the Invention) According to the present invention, it is possible to improve the properties of graphite powder very easily, and the improved graphite powder obtained has a large specific surface area, liquid retention rate, and cohesive force, and has excellent formability and lubricity. It has excellent electrical resistance and low coefficient of friction, and can be suitably used for applications such as conductive materials for dry batteries, sliding members, pencil leads, and silicon carbide production.

Furthermore, if artificial graphite is used as a raw material, it is possible to easily and stably produce graphite that contains very few impurities, especially metal impurities, and has performance equivalent to or better than natural flaky graphite, and contains such improved graphite powder. The dry battery of the present invention exhibits equivalent characteristics that are easy to manufacture and have a long life, and the sliding member of the present invention also has sufficiently improved characteristics such as lubricity, mold releasability, abrasion resistance, and friction resistance. Both offer significant industrial benefits.

Claims (3)

[Claims] (1) Improved graphite powder obtained by pulverizing graphite mainly by shearing force parallel to the plane of the carbon network of the graphite. (2) A dry battery containing, as a conductive material, improved graphite powder obtained by pulverizing graphite mainly by shearing force parallel to the plane of the carbon network of the graphite. (3) A sliding member containing improved graphite powder obtained by pulverizing graphite mainly by shearing force parallel to the plane of the carbon network of the graphite.