JPH02204317A - Graphite powder and lubricant and black ink using the same - Google Patents

Abstract

PURPOSE:To obtain the highly bearing graphite powder excellent in lubricity by specifying the aspect ratio of the crystal grain and the grain diameter of the powder. CONSTITUTION:The aspect ratio (the thickness of the crystal grain in the direction at right angles to the C axis divided by that in the C axis direction) of the crystal grain of graphite powder is controlled to 1.1-2.0, the average grain diameter of the powder is controlled to 1.4-2.5mum, and the powder consists of the almost lumpy fine grains and is excellent in lubricity. The fine-grain graphite is obtained by dry-crushing the common scaly graphite powder having about 5-50mum average grain diameter as the starting material by a vibrating mill. In that case, the crushing is preferably carried out in a reduced-pressure crushing chamber. The graphite powder is dispersed in a liq. dispersion medium when used as a lubricant. Water or an org. agent is used as the dispersion medium for the lubricant in the plastic working of metal, and oil is used for the lubricating oil of gears, etc. Meanwhile, the graphite powder is added into the vehicle of the black ink for the printing ribbon of a dot printer to reduce the abrasion loss of the dot wire.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a fine particle graphite powder having excellent lubricating properties, a lubricant using the same, and an ink for a printing ribbon of a dot printer.

[Prior Art J] One of the properties of graphite is interfoldability, and this property is utilized as a solid lubricant.

Graphite for lubricants is desirably present uniformly on the lubricated surface, and is generally used in the form of fine particles.

Fine particles of graphite can be obtained by dry or wet ball milling, and a vibrating ball mill is often used for shooting.

The shape of crushed graphite powder is thin plate-like (scale-like), and it is easy to blue the lubricated surface, and it is said that the lubricity between the folds is good.It is also heat resistant, so it can be used in high-temperature environments. Lubricants for sliding parts used, press lubricants for hot forging of metals,
Used as a lubricant for high surface pressure sliding parts.

[Problem to be solved by the invention]

However, in this case, as the applications have diversified, there has been an evaluation that the desired lubrication effect cannot be obtained, especially in high surface pressure lubrication applications, making it difficult to expand the range of applications.

This invention was made with the aim of improving the quality of graphite lubricants by further bringing out the lubricating properties of graphite, and thereby expanding its uses.

[Means for Solving the Problems] While considering the mechanism of solid lubrication, the inventors discovered that the shape of graphite particles and the shape of crystal particles control a considerable part of the lubricity. The conventional problems have been solved by changing the crystal grain shape from the conventional scale-like shape to a mass-like shape.

That is, this graphite powder has a crystal particle shape ratio (X!! refers to the ratio of the thickness in the direction perpendicular to the C-axis to the thickness in the C-axis direction measured by diffraction analysis) of 1.1 to 2.0. The average particle size of the powder is 1.4 to 2.5 μm.

Examples of applications include using water or an organic agent as a dispersion medium,
Lubricants used in dry lubricant films for plastic processing of metals and camera zoom mechanisms, etc. Oil is used as a dispersion medium, as well as coating lubricants used as lubricants for gears, bearings, and machine elements, as well as dot printers. Examples include adding it to black ink for printing ribbons.

Incidentally, the amount of graphite added in the above-mentioned application examples ranges over a wide range from several percent to several tens of percent depending on the purpose of use industrially, and the amount added is not particularly limited in the present invention.

[Production] The graphite for lubricant according to the present invention has a shape ratio of crystal particles of 11.
~2.0, and the average particle size of the powder is 1.4~2.5μ
It is m.

The lubricating properties show better performance as the shape ratio of the crystal particles approaches 1, but the lower limit should be kept at 1.1 in consideration of the crushing ratio for obtaining the particle size, which will be described later. When the shape ratio of crystal particles exceeds 2, the properties are no different from those of conventional flaky graphite powder.

That is, the shape of conventionally used graphite crystal particles is one-handed, and l'111! Graphite attached to a surface is less likely to cause interfolding and movement of crystals due to stress in the frictional direction, but in the case of graphite with a shape ratio of crystal grains close to 1, interfolding and particle movement are more likely to occur. It is thought that the lubricating properties are deteriorated due to the combination of these two factors.

Furthermore, in addition to the shape ratio of the crystal particles described above, the average particle diameter (in other words, specific surface area) also affects the lubricating properties.

When the thickness is 2.5 μm or less, the lubricity is good. When the size exceeds 2.5 μm, the shape ratio of crystal particles exceeds 2, and the properties are not much different from those of conventional graphite powder.

On the other hand, it is said that the smaller the average particle size of graphite powder (the larger the specific surface area), the more preferable it is as a lubricant. However, production efficiency is poor and this is not desirable.

In order to obtain fine particle graphite with good lubricity in the present invention, dry pulverization is carried out using a vibrating mill, and at this time, the pressure inside the pulverization chamber is actively reduced using a vacuum pump, or the pulverization chamber is kept in a sealed state.

When graphite is crushed under reduced pressure by taking advantage of gas adsorption of graphite due to an increase in specific surface area during the crushing process, the particle shape of the crushed graphite and the shape of the crystal particles become close to block-like.

As the graphite powder to be crushed (starting material), a commercially available graphite powder having an average particle diameter of about 5 to 50 μm is used.

f Example] First, as shown in Table 1, Example graphite powder A-Ci3 and Comparative Example DG of the lubricant of the present invention were prepared.

The graphite powder to be crushed was natural flaky graphite having an average particle diameter of 8.8 μm, a specific surface area of 3.5 rn''/g, and a crystal particle shape ratio of 2.6.

Here, the average particle diameter refers to the average value obtained by measuring the particle size distribution of powder by an electrical resistance method called a Coulter counter, and the specific surface area refers to the value measured by a normal specific surface area meter using the BET method, and the crystal grain The shape ratio is the value obtained by dividing the crystal grain thickness in the direction perpendicular to the C-axis by the crystal grain thickness in the C-axis direction, as measured by X-ray diffraction analysis as described above.

In addition, the average particle diameter is about 2.0 mm when measured by a light transmission method.
It tends to show a value about four times larger.

Further, the specific surface area of wet-pulverized sample G was not measured because it was difficult to remove water, but for xi diffraction, the slurry was neutralized and dried under reduced pressure and then measured.

The vibration mill used is a mechanism that generates vibrations by eccentrically rotating a cylindrical crushing chamber in the circumferential direction, and steel balls are placed inside the cylindrical chamber.

There is a material inlet/outlet at the top of the grinding chamber, which can be covered and sealed with a lid with a valve.

In pulverizing the graphite powder to be crushed under the pulverizing conditions shown below, pulverized graphite samples A-C were dry-pulverized in a closed crushing container, samples D-F were dry-pulverized with a valve open, and G is obtained by adding water to the graphite powder to be ground and grinding it into a slurry.

Internal volume of crushing container: 3.4 liters Steel ball diameter: 10mm Filling amount of steel balls: 68% Graphite powder input fl: 600g Vibration R: 1600cpm Amplitude: 7mm Table 1 shows the properties of each crushed graphite sample.

Looking at Samples A to C, it can be seen that the powder particles are finer than the other samples, and the shape ratio of the crystal particles is small, that is, they are lumpy. The crystal grain has a thickness of 240 to 40 mm in the direction perpendicular to the C axis.
0 person, and the thickness in the C-axis direction is 185 to 220 people.

Samples D-F are pulverized with the pulverization time, but the shape ratio of crystal particles is about 2, and sample G has a shape ratio of 3 or more.

Table Example-1 (Forging lubricant) Next, 3% by weight of each of the seven types of fine graphite of Samples A to G, carboxymethyl cellulose (CMC) 1
% and residual water, and each was applied to hot forging.

Figure 1 is a cross-sectional view of the main parts explaining the forging method.

(a) shows the state before pressurization, and (b) shows the state after pressurization. The forged product 1 has a gear 3 on the outer periphery of the flange 2, and the gear 3 before forging has a smaller diameter than the cavity of the mold 5, and is compressed in the axial direction and plastically deformed in the radial direction. The tooth portion 4 after compression has an R-shape on the lower side in the figure. Material is S
A CM2O1N material was used.

After heating the pressing mold 5 to 150°C and applying the lubricant to the cavity surface 6 of the pressing mold 5, the forged product 1 heated to 800°C is placed in the cavity, and the pressing speed is set to 100 mm.
/second, and the amount of axial deformation was 15%.

Then, as shown in Fig. 2, the curvature dimension of the tooth section 7 of the press die 5 and the curvature dimension of the tooth section 8 of the forged product are taken, and the ratio is expressed as a percentage to determine the lubricity (hereinafter referred to as R accuracy rate). evaluated.

Here, r: radius of curvature of the teeth of the die X: length of the curvature of the teeth of the forged product in the X direction Y: length of the curvature of the teeth of the forged product in the Y direction This indicates that the forged product 1 is plastically flowing on the cavity surface 6 of the figure, indicating that the lubricant has good characteristics.

Figures 3 and 4 are graphs of the results.
The shape ratio of crystal particles is 2 or less, and the average particle shape is 265
The lubricants of samples A-C below μm are excellent. It can be seen that even if the average particle diameter is 2.5 μm or less as in sample F, the lubricating properties are poor if the crystal grain shape ratio exceeds 2.

Next, using an organic agent as a dispersion medium for graphite, a lubricant was prepared by adding 10% polymethyl methacrylate and 20% fine graphite to a 70% mixed solvent of toluene, xylene, and methyl ethyl ketone, and the cold plasticity Applied to processing.

Composition is 0.2% C, 2% Ni, 0.5% Mo, balance Fe
After applying the above-mentioned lubricant on the surface of a cylindrical sintered alloy having a density of 6-6 g/crd and drying it.

A comparison of the extrusion loads during forward extrusion plastic working with a cross-section reduction rate of 20% showed the same tendency as described above.

Example 2 (Lubricant) Among the seven types of graphite of Samples A to G, graphite of Samples B and E was prepared, and SAE 15W-50 mineral oil (API S
F grade) with 2.5% graphite and 0.0% dispersant by weight.
2% was added.

The test equipment used was Falex Model No.
This testing machine is equipped with a rotating ring half immersed in test oil and a block that is pressurized above and in contact with the ring, and can measure the coefficient of friction and oil temperature between the two.

The rotating ring increases the rotation speed linearly from a stopped state to 1
After 5 minutes, the speed was increased to 4300 rpm, and then the speed was increased to 1 rpm at the same speed.
It was maintained for 5 minutes. The sliding speed at this time was 7.85 m/
Second, the load on the block is 27.3 kg.

FIG. 5 is a graph showing the results, in comparison with mineral oil without graphite added. It can be seen that the graphite-added lubricating oil has a small increase in oil temperature and a small friction coefficient, and in particular, the one using graphite of sample B, which has a small particle size and a small crystal grain shape ratio, is excellent.

Such a graphite-dispersed lubricating oil is suitable for gear lubrication, bearing lubrication, etc., such as engine oil.

Example 3 (Ink for ink ribbons) Next, out of the seven types of graphites of Samples A to G, the graphites of Samples B and E were added to the ink for ink ribbons of a dot printer, and the ink was made into a dot printer with a width of 13 mm and a length of 13 mm. A printing test was conducted by impregnating a 15 m long endless nylon base fabric. When the number of printed characters reached 100,000 characters, the ribbon was replaced with a new ribbon of the same type, and three square characters were printed on each ribbon.

Table 2 shows the composition of the ink and the wear amount of the dot wire length after printing. Sample P is the same as sample B with graphite added, sample Q is the same as sample E with graphite added,
The sample FlR does not contain graphite. The amount of graphite added is
It replaced a portion of the coloring material carbon black to 3%.

This experimental method is the same as that described in Japanese Patent Application Laid-Open No. 59-86671, and the purpose is to prevent the wire from being worn out, since wear of the dot wire has become a problem as the printing speed of printers increases. The goal was to develop an ink ribbon.

According to the printing test results shown in Table 2, Sample R, which does not contain graphite, has the largest amount of wire wear. Addition of graphite significantly reduces the amount of wire wear, and Sample P is judged to be the best.

[Effect of the Invention I As explained above, the present invention further exhibits the excellent lubricity of graphite by using fine graphite powder having a specific crystal grain shape and a specific average particle diameter. Therefore, it will improve the quality of currently used graphite-containing lubricants and greatly contribute to industries seeking reduced friction.
The effects of this technology are extremely large, as it has expanded its application to industrial fields that had been evaluated as not meeting the required characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts explaining the hot forging method of the example,
Figure 2 is an explanatory diagram of the R accuracy rate in a construction, Figure 3 is a graph showing the relationship between the shape ratio of graphite crystal particles and the R accuracy rate, and Figure 4 is the relationship between the average particle diameter of graphite and the R accuracy rate. Figure 5 is a graph showing the oil temperature and friction coefficient based on the Farex model of lubricating oil and one test. l... Forged product 2... - Flange 3... Gear 4... Teeth 5... Press die 6... Cavity surface 7... Press tooth part 8... Wave manufactured product Hitachi Powder Metallurgy Co., Ltd.

Claims (1)

[Claims] 1. The shape ratio of the crystal grains (thickness in the direction perpendicular to the C-axis of the crystal grains÷thickness in the C-axis direction) is 1.1 to 2.0, and the average particle diameter of the powder is Graphite powder characterized by having a particle size of 1.4 to 2.5 μm. 2. A lubricant characterized by dispersing the graphite powder according to claim 1 in a liquid dispersion medium. 3. The dry film-forming lubricant according to claim 2, wherein the dispersion medium is water or an organic agent. 4. The lubricant for mechanical elements according to claim 2, wherein the dispersion medium is oil. 5. A black ink for a printing ribbon for a dot printer, characterized in that the graphite according to claim 1 is added to the vehicle in a printing ink comprising a coloring material that exhibits a desired color tone dispersed in a vehicle.