JP2008125320A - Metal graphite material, manufacturing method therefor and brush for dc motor using metal graphite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal graphite material that is superior in electrical conductivity having a small quantity of copper, a manufacturing method therefor, and a brush for a DC motor of which the contact voltage drop is low, motor efficiency is high, slidability is satisfactory, a friction variation is reduced, and reduced in wear under a high load and in a high temperature. <P>SOLUTION: The metal graphite material has as the main component graphite and copper obtained by firing graphite powder mixed, granulated and molded with fine copper fine particles. Furthermore, the metal graphite material has a conductive passage among the graphite powder by bringing a part of the surface of the graphite powder into contact with the copper fine particles to make them adhere to one another and electrically combining the graphite power by the copper fine particles. A method of manufacturing the metal graphite material is also provided, and further, a brush for DC motor is provided that uses the metal graphite material manufactured by the manufacturing method therefor is also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a metallic graphite material mainly composed of graphite and copper, a method for producing the same, and a brush for a DC motor using the metallic graphite material.

  In recent years, various motors including those for automobile electrical equipment are strongly demanded to reduce the size of the motor in order to reduce the load weight, and the use of a small motor having a large output is increasing. In a DC motor with a brush, the rotor, magnet, and the like can be reduced in size by structural ingenuity and optimization, but a brush that must allow for the wear allowance is limited in reducing the size and shape.

Further, since the upper limit of the use temperature must be increased due to the increase in motor output, it is necessary to suppress brush wear at high temperatures.
On the other hand, motors for automobile electrical equipment have a strong need for noise reduction in the vehicle and are required to reduce the sliding noise of the motor as much as possible.

  Conventionally, brushes for direct current motors have been made of metallic graphite material, mainly natural graphite coked with binders such as copper powder and resin, and metal additives such as lead, tin, zinc, and various alloy powders. After being mixed and molded, it was obtained by firing.

In general, in order to increase the motor output, the amount of copper contained in the brush is increased to lower the electrical resistance of the brush, thereby reducing the contact voltage drop between the brush and the commutator.
However, in this method, there is a problem that the slidability is deteriorated due to the contact between the copper in the brush and the copper in the commutator, and wear of both the brush and the commutator is increased.

  In addition, in order to improve the wear resistance at relatively high temperatures, there are those to which a small amount of metal sulfide powder such as molybdenum disulfide and tungsten disulfide is added, but when the brush temperature is further increased, these metal sulfides As a result of modification due to oxidation or the like, the properties of grindability appear, and there is a disadvantage that the lubrication is insufficient, brush wear increases, the specific resistance increases, and the electrical loss increases.

In order to reduce wear caused by spark discharge, which is another cause of brush wear, copper particles are dispersed across the graphite particles, forming a continuous copper particle conductive path that conducts charge rather than an isolated structure of copper particles. A method is proposed in which a copper complex salt solution is applied to the surface of graphite particles, and an aggregate of graphite particles forming a coating film is baked in an oxygen-containing atmosphere and then heated in a reducing atmosphere. (For example, refer to Patent Document 1).
JP 2005-012957 A (page 4-6)

  However, in order to reduce the electric resistance of the brush, continuous contact between the copper fine particles is necessary, and the amount of the copper fine particles is relatively increased. As shown in FIG. 2, the amorphous carbon 3 having poor electrical conductivity is used as a binder to fix the copper fine particles 1 to the graphite particles 2, so that the conduction between the copper fine particles 1 and the graphite particles 2 is caused by the amorphous carbon 3. This is because the passage is blocked. As a result, since the amount of copper particles must be increased, the friction coefficient of the metal graphite material is high and wear increases.

The present invention provides a metallic graphite material having a small amount of copper and excellent electrical conductivity, and a method for producing the same.
Further, the present invention provides a brush for a DC motor having a low contact voltage drop, high motor efficiency, good slidability and less frictional fluctuation, and less wear under high load and high temperature. It is to provide.

The present invention relates to a metal graphite material mainly composed of graphite and copper obtained by mixing, granulating, forming, and firing graphite powder and copper fine particles, and contacting the copper fine particles with a part of the surface of the graphite powder. It is related with the metal graphite material which made it adhere and was made to electrically couple | bond graphite powder with copper microparticles | fine-particles, and formed the electrical conduction path between graphite powder.
The present invention also relates to the above-mentioned metal graphite material having a structure in which graphite powders to which copper fine particles are fixed are fixed using amorphous carbon as a binder.

  In addition, the present invention mixes a solution in which a copper complex salt is dissolved and graphite powder so as to disperse each other, and after removing the solvent and drying the obtained mixture, pre-baking in an inert atmosphere is performed from the copper complex salt. The present invention relates to a method for producing a metallic graphite material, wherein copper fine particles are deposited and the deposited copper fine particles are fixed to a graphite powder.

  The present invention also includes a solution in which the copper complex salt is dissolved and the graphite powder are mixed so as to disperse each other, and the resulting mixture is desolvated and dried, and then pre-fired in an inert atmosphere to precipitate from the copper complex salt. A step of fixing the fine copper particles to the graphite powder, a step of forming a granulated powder by adding a resin binder to the fixed copper and graphite powder, and heating a molded body obtained by molding the granulated powder in a mold in a non-oxidizing atmosphere And firing the metal graphite material.

The present invention also relates to the above-described method for producing a metallic graphite material, wherein a surfactant is added when mixing a solution containing a copper complex salt and graphite powder.
Moreover, this invention relates to the manufacturing method of the said metal graphite material whose copper complex salt is copper acetate.

Moreover, this invention relates to the manufacturing method of the said metal graphite material whose temperature which pre-bakes mixed powder in inert atmosphere is 250 to 400 degreeC.
Moreover, this invention relates to the manufacturing method of the said metal graphite material whose temperature which bakes a molded object in a non-oxidizing atmosphere is 350 to 1000 degreeC.

  Furthermore, the present invention relates to a brush for a direct current motor using the metal graphite material or the metal graphite material produced by the method.

The present invention can obtain a metal graphite material having excellent electrical conductivity even with a small amount of copper.
In addition, the present invention has a low contact resistance with the commutator, can reduce the contact voltage drop of the motor, can increase the efficiency of the motor, and can relatively increase the blending amount of graphite, so that the slidability It is possible to obtain a brush for a direct current motor that is excellent in resistance and has little mechanical wear.
Furthermore, the brush for a DC motor obtained by the present invention has fine copper fine particles dispersed and fixed to primary graphite particles, so that the commutator sliding traces are uniform, there is no abnormal wear, and the friction fluctuation is small. Stable sliding is obtained.

  In the present invention, in order to make graphite particles act positively as a conductive medium, a small amount of copper fine particles are interposed between the graphite particles and the graphite particles are as if they were electrodes of individual graphite particles. Electrically couple particles together.

  The crystal structure of graphite is hexagonal, and carbon electrons are π-conjugated in a plane perpendicular to the c-axis, that is, in the plane of a so-called graphene sheet, and thus show high electrical conductivity. The conductivity is very low. For this reason, in order to ensure electrical conductivity between graphite particles whose crystal axes are randomly oriented, the graphene sheets of the graphite particles must be electrically connected to each other.

  In the present invention, in a state where the copper complex salt solution is sufficiently in contact with the graphite particle surface in advance, the copper fine particles are directly deposited on the surface of the graphite particle by heating in an inert atmosphere. As a result, at least one copper fine particle is fixed to a part of the surface of the graphene sheet of graphite particles.

For this reason, it is desirable that the deposited copper fine particles are smaller than the particle size of the graphite particles, and the effect per unit weight of copper in the metal graphite material is great.
The particle diameter of the copper fine particles formed in the present invention is preferably 0.01 to 20 μm, and more preferably 0.1 to 5 μm. On the other hand, the particle size of the graphite particles is preferably 1 to 200 μm, and more preferably 5 to 100 μm because the effect of the present invention is most prominent.

  The amount of copper particles in the entire composition is preferably 5 to 50% by weight, and more preferably 10 to 40% by weight because the effects of the present invention are easily manifested. If it exceeds 50% by weight, the friction coefficient tends to increase and wear tends to increase. On the other hand, if it is less than 5% by weight, the electric conductivity tends to be not sufficiently reduced as a metallic graphite material.

In addition, it is not necessary for all the copper fine particles precipitated by the production method of the present invention to be precipitated on the surface or end of the graphene sheet of graphite particles, and even if the copper fine particles are partially aggregated, the effect is not lost.
In the present invention, as shown in FIG. 1, it is necessary that the graphite particles 2 and the copper fine particles 1 are in direct contact to maintain electrical conductivity. For this reason, in this invention, it is desirable to use the copper complex salt from which copper precipitates directly, without passing through a transient intermediate compound by thermal decomposition. In FIG. 1, 3 is amorphous carbon.

  Examples of the copper complex salt on which copper is directly deposited include a copper carboxylate, and copper complex salts such as formic acid, acetic acid, propionic acid, butanoic acid, oxalic acid, malonic acid, and glutaric acid are used. In these copper complex salts, fine particles of metallic copper are directly deposited by thermal decomposition and decompose without going through copper oxides or hydroxides. These copper complex salts dissolve in water or alcohol and are added to graphite to be well dispersed. At this time, when a surfactant is added to water or alcohol, the copper fine particles are easily dispersed and precipitated.

  A nonionic surfactant can be used as a surfactant to be added at the time of mixing the solution in which the copper complex salt is dissolved and the graphite powder, and the amount added is 0.001 to 0.001 to the solution in which the copper complex salt is dissolved. 0.5% is preferable.

  Nonionic surfactants include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene alkyl ether, polyoxyethylene myristyl decyl ether, polyoxyethylene octyl Dodecyl ether, alkylene alkyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene distyrenated phenyl ether, polyoxyethylene tristyrenated phenyl ether, polyoxyethylene benzyl phenyl ether, polyoxyethylene derivative, polyoxyethylene polypropylene glycol However, polyaromatic polyoxyethylene ethers are the most preferred of the present invention. Easily elicit fruit, in particular, polyoxyethylene styrenated phenyl ether, polyoxyethylene distyrenated phenyl ether, polyoxyethylene tristyrenated phenyl ether, polyoxyethylene benzyl phenyl ether.

  The dispersion of the graphite in the solution in which the copper complex salt is dissolved needs to sufficiently stir the mixture, but it is easy to disperse by applying ultrasonic waves from the outside. The mixture is dehydrated or dealcoholated in an oven at 35 to 75 ° C. with an evaporator and then dried at 100 to 120 ° C. under reduced pressure or in an inert atmosphere such as nitrogen or argon. Furthermore, it bakes at 300-350 degreeC in the electric furnace of an inert atmosphere, and decarboxylates or carboxylic acid is decomposed | disassembled.

  The powder obtained by adhering the copper fine particles obtained by the present invention to the graphite particles and being integrated is different from a mixture of the copper fine particles and the graphite particles. That is, the powder produced in the present invention has a property that the copper fine particles and the graphite particles are difficult to separate even by vibrations generated in unit operation steps such as powder mixing and molding.

The dried powder is added with a resin binder and a solvent in which the resin binder is dissolved and mixed well with a kneader, then transferred to a container and dried at 60 to 120 ° C. to evaporate the solvent.
As the resin binder, resol phenol resin, novolak phenol resin, modified novolac phenol resin, furan resin, or the like can be used.

  Solvents include aliphatic low-boiling alcohols such as methanol, ethyl alcohol and propanol, ketones such as acetone and methyl ethyl ketone, and high-boiling aromatic alcohols such as furfuryl alcohol, phenol and cresol, or a mixed solvent thereof. Used.

  The dried mixture is classified through a sieve, and then the classified powder is blended at a predetermined ratio. This powder is put into a mold and pressed with a molding machine to form a molded body, and then fired in a firing furnace in an inert atmosphere or a reducing atmosphere. Nitrogen, argon, or the like can be used as the inert atmosphere, and hydrogen, propane-modified gas, or the like can be used as the reducing atmosphere. The firing temperature is preferably 400 to 1000 ° C.

  In the above description, the method for obtaining a molded body and a fired body by adding only a powder in which copper fine particles are fixed to graphite particles and adding a binder thereto is described. However, molding and firing may be performed without adding a binder. That is, by adjusting the amount of moisture at the time of drying, etc., without adding a resin binder, the powder itself in which the copper fine particles are fixed to the graphite particles can be formed and fired to obtain a fired product.

  In addition, powder with copper fine particles fixed to graphite particles, another new graphite powder, carbon powder, etc. or copper powder such as electrolytic copper, ground copper powder, molybdenum disulfide, tungsten disulfide, metal, metal An additive such as a compound can be added to adjust the composition to obtain a fired body. Other substances such as the above-mentioned additives may be added when preparing a powder in which copper fine particles are fixed to graphite particles, or may be added later when a binder is added.

Examples of the present invention will be described below.
Example 1
In a flask, a commercially available copper (II) acetate hydrate Cu (CH ₃ COO) ₂ .H ₂ O was dissolved in 11 times by weight of water, and 0.05 wt% of a surfactant (made by Kao, trade name Emulgen) A-500, polyoxyethylene distyrenated phenyl ether) was added to prepare a copper acetate aqueous solution of about 8 wt%.

  To this solution, graphite powder was added so that the final weight composition of copper would be 20% and mixed well. After 20 minutes in an ultrasonic device for sufficient mixing, the pressure was reduced using an evaporator with an aspirator, and the sample in the flask was heated to 55 ± 20 ° C. with a thermo bath to sufficiently evaporate the water.

  The powder in the flask was further dried in a vacuum dryer at 100 ° C. and 0.1 Pa for 3 hours, and then this powder was placed in a boat and temporarily placed in a tubular electric furnace at 330 ° C. for 1 hour in a nitrogen atmosphere. Baked,

On the other hand, the novolak phenol resin was dissolved in a small amount of methanol to make a paste, and this paste and the powder after deacetic acid pre-baked above were mixed in a mortar.
Next, the mixture was transferred to a container, left in a thermostatic bath at 60 ° C. for 3 hours, and methanol was evaporated to obtain a mixed powder.

The mixed powder was sieved with a sieve of 63 μm, 126 μm and 425 μm, and a powder of 63 μm or less: a powder between 63 and 126 μm: a powder between 126 and 425 μm was blended at a weight ratio of 1: 1: 1. This blended powder was put into a mold to produce a rectangular molded body at 196 MPa (2 t / cm ² ). This molded body was set in an electric furnace and fired at 700 ° C. for 1 hour while flowing nitrogen gas. Thereafter, a test piece of 5 mm × 7 mm × 10 mm was cut out from the molded body and subjected to a sliding test.

Example 2
A test piece was prepared through the same steps as in Example 1 except that firing was performed at 1000 ° C. for 1 hour in an electric furnace in which nitrogen gas was passed.

Example 3
A test piece was prepared through the same steps as in Example 1 except that the baking was performed at 1100 ° C. for 1 hour in an electric furnace in which nitrogen gas was passed.

Example 4
A test piece was prepared through the same steps as in Example 1 except that the baking was performed at 1100 ° C. for 3 hours in an electric furnace in which nitrogen gas was passed.

Comparative Example 1
In a flask, commercially available copper acetate (II) hydrate Cu (CH ₃ COO) ₂ .H ₂ O was dissolved in water 11 times by weight to prepare an about 8% copper acetate aqueous solution. Subsequently, the solid novolak phenol resin was dissolved in a small amount of methanol, and this was mixed with the previously prepared copper acetate aqueous solution.

  Furthermore, after adding 0.05 wt% of a surfactant (trade name Emulgen A-500, manufactured by Kao, polyoxyethylene distyrenated phenyl ether) and graphite powder and mixing thoroughly, the mixture was stirred in an ultrasonic device for 20 minutes. Went.

  The prepared sample was depressurized using an evaporator with an aspirator, and the sample in the flask was heated to 55 ± 20 ° C. with a thermo bath to sufficiently evaporate methanol and moisture. The powder was transferred to a porcelain container and pre-baked in a tubular electric furnace at 330 ° C. for 1 hour while flowing nitrogen gas, and deaceticated.

Next, this powder was put into a mold to produce a rectangular molded body at 196 MPa (2 t / cm ² ), and fired at 700 ° C. for 1 hour in a nitrogen atmosphere. Thereafter, a test piece of 5 mm × 7 mm × 10 mm was cut out from the molded body and used for the test.

Comparative Example 2
In Comparative Example 1, a powder obtained by evaporating methanol and water using an evaporator was molded at a pressure of 16.7 × 10 ³ Pa (0.17 Kg / cm ² ), and the molded body was subjected to nitrogen gas in a tubular electric furnace. Was calcined at 330 ° C. for 1 hour and deaceticated. Except that, a test piece was prepared through the same steps as in Comparative Example 1.

Comparative Example 3
In Comparative Example 1, after sufficiently evaporating methanol and water using an evaporator, it was further dried in a vacuum dryer at 110 ° C. for 1 hour, and this powder was heated at 330 ° C. while flowing nitrogen gas in a tubular electric furnace. Temporary calcining for an hour and deacetication. Except this, the test piece was produced through the process similar to the comparative example 1.

Next, the comparative tests shown below were performed using the test pieces obtained in Examples 1-4 and Comparative Examples 1-3. The results are shown in Tables 1 and 2.
The specific resistance was measured by the 4-terminal method. In a state where the metal electrode plate is pressed on both sides of a test piece having a thickness of 5 mm, a width of 7 mm, and a length of 10 mm, a constant current is passed, and two styluses (distance between stylus: 10 mm) are placed on the upper surface of the test piece. The voltage between the two styluses was measured with a multimeter. The specific resistance was determined from this.

  The bending strength is set so that the pressing direction during molding of the metal graphite powder becomes the thickness of the test piece, and the metal graphite molded body has a thickness (H) of 4.5 mm and a width (W) of 7.2 mm. The test piece was cut into a length of 17 mm, and this test piece was tested at a constant speed load of 2.3 mm / min with a load-to-fulcrum distance (L) set to 10 mm using an autograph bending tester. After measuring the bending load (P), it was calculated by the following formula.

The hardness was measured using a Shore C type hardness tester manufactured by Imai Seiki.
In the abrasion test, two brushes (test pieces) were opposed to each other so as to face a copper slip ring having a rotational speed of 1420 min ⁻¹ (7.4 m / s), and the brush was fixed with a spring at a constant pressure of 4.5 N (450 g). ) / A brush was brought into contact, and after 45 hours of operation, the amount of wear of the test piece when not energized and when energized (8A) was measured. For energization, two brushes (test pieces) via a copper slip ring were used as ± poles, and 8 A was energized between them. The amount of wear during no energization and during energization was calculated as a value per 100 hours.
Further, the voltage drop (contact voltage drop) between the brush and the copper slip ring was measured during energization.

  As shown in Table 1, the metal graphite materials obtained in Examples 1, 2, 3, and 4 were more specific resistance and bending strength than the metal graphite materials obtained in Comparative Examples 1, 2, and 3. It is clear that this is superior.

  As shown in Table 2, the metal graphite brushes obtained in Examples 1, 2, 3 and 4 were compared with the metal graphite brushes obtained in Comparative Examples 1, 2, and 3 when no current was applied and when the current was not supplied. It is clear that the amount of wear at the time is low and the voltage drop is excellent.

It is a schematic diagram of the structure of the metal graphite material which becomes an Example of this invention. It is a schematic diagram of the structure of the conventional metal graphite material.

Explanation of symbols

1 Copper Fine Particle 2 Graphite Particle 3 Amorphous Carbon

Claims (9)

  In a metallic graphite material mainly composed of graphite and copper obtained by mixing, granulating, molding and firing graphite powder and copper fine particles, the copper fine particles are brought into contact with and fixed to a part of the surface of the graphite powder. A metal graphite material in which graphite powders are electrically bonded with copper fine particles to form a conductive path between the graphite powders.   The metal graphite material according to claim 1, which has a structure in which graphite powders to which copper fine particles are fixed are fixed with amorphous carbon as a binder.   After mixing the solution in which the copper complex salt is dissolved and the graphite powder to disperse each other, the resulting mixture is desolvated and dried, and then pre-fired in an inert atmosphere to precipitate copper fine particles from the copper complex salt, A method for producing a metallic graphite material, wherein the deposited copper fine particles are fixed to a graphite powder.   The copper complex salt-dissolved solution and the graphite powder are mixed so that they are dispersed with each other, and the resulting mixture is desolvated and dried, and then pre-fired in an inert atmosphere to precipitate the copper fine particles precipitated from the copper complex salt. The step of adhering to copper, the step of forming a granulated powder by adding a resin binder to the adhering copper and graphite powder, and heating and firing a molded body obtained by molding the granulated powder in a non-oxidizing atmosphere. A method for producing a metal-graphite material.   The method for producing a metallic graphite material according to claim 3 or 4, wherein a surfactant is added when the solution containing the copper complex salt and the graphite powder are mixed.   6. The method for producing a metallic graphite material according to claim 3, 4 or 5, wherein the copper complex salt is copper acetate.   The method for producing a metallic graphite material according to any one of claims 3 to 6, wherein the temperature for pre-baking the mixed powder in an inert atmosphere is 250C to 400C.   The method for producing a metallic graphite material according to claim 4, 5 or 6, wherein a temperature at which the compact is fired in a non-oxidizing atmosphere is 350 ° C. to 1000 ° C.   A brush for a direct current motor using the metal graphite material according to claim 1 or 2 or the metal graphite material produced by the method according to any one of claims 3 to 8.

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