DE2040695C3 - Process for the production of oleophilic graphite - Google Patents

Description

20th

The invention relates to a method for producing oleophilic graphite by grinding graphite in an organic liquid as well as the use of the oleophilic graphite obtained in this way for the production of 2s of thickened lubricating oil.

British Patent 11 68 785 describes the Manufacture of oleophilic graphite by grinding the graphite in an organic liquid The British Patent 11 68 764 describes the use of oleophilic graphite as a thickener for lubricating greases.

According to FR-PS 15 00 361 and 15 78 534, the oleophilic graphite by grinding graphite in a Vibratory ball mills manufactured Vibratory ball mills, however, consume a relatively large amount of energy for the Production of oleophilic graphite. The grinding effect comes from the impact of the balls on each other and on the case. The greater the oscillation amplitude, the more effective the grinding. With more viscous Milling liquids, the efficiency of milling is lower, so that it is advantageous in low-viscosity Grind liquids.

If the oleophilic graphite is to be used as a thickening agent for lubricating greases, it is convenient to use at least a portion of the base oil as milling liquid alone or mixed with an easily removable, miscible diluent. In the case of vibratory ball mills, this would require the use of very high milling temperatures in order to lower the viscosity of the milling liquid to an acceptable level. The use of high milling temperatures complicates the problems and increases the difficulty and can cause the lubricating oil to degrade. Furthermore, liquids that are volatile at high temperatures cannot form part of the grinding liquid. Oleophilic metal sulfides and greases thickened with oleophilic metal sulfides can be prepared by processes similar to those used for oleophilic graphite. _b o

It has now been found that products with surprisingly advantageous properties are obtained which are superior to the previously known products if natural or synthetic graphite, optionally also together with metal sulfides, is measured in an organic liquid with a viscosity of 85 to 1000 cP a shear rate of 511 sec- ¹ at 25 ° C grinds and an agitator

mill used

An agitator mill is to be understood as a mill in which the grinding is carried out by stirring the Grinding media by rotating an axis to which the projections are attached, takes place for the Agitator mills suitable for the purposes of the invention is the axis in a housing on airtight bearings mounted High density balls, e.g. made of steel or zirconium, are preferably used as grinding media preferably have an average diameter of less than 5 mm. The housing is made of steel

The projections on the axis can, for example, be in the form of discs, rods, or paddles Propellers or any other shape. In the mills preferred according to the invention, there are Projections made from parallel disks.

All organic liquids that do not react with the graphite are suitable as grinding liquids. Preferably, compounds or mixtures of compounds are used which are obtained by distillation of petroleum. Preferred as milling liquid paraffinic hydrocarbons which are preferably above boiling from 100 ⁰ C.

The solids can be ground in batches by using the mill with the grinding media attached to it grinding solid and the organic liquid is filled, making sure that the mill for Avoiding contamination with air is completely filled with liquid. The mill is then left one run for a certain time, after which the slurry of organic milling liquid and milled solid is separated from the grinding media.

Agitator mills are usually designed to operate within preferred viscosity ranges During the grinding, the viscosity of the grinding liquid increases as a result of the action of the ground Solids. In order to maintain optimal grinding conditions, the grinding liquid can be used during the Be diluted by grinding. If grinding is carried out in a mixture of oil and volatile liquid, the Dilution can be done by adding further amounts of a mixture of these liquids. If in In the presence of oil alone, additional oil can be added to the milling process To keep viscosity between the desired limits.

In a preferred embodiment, the mill is operated in a cyclical process. At this Embodiment, the mill forms part of the closed circuit in which the organic Milling liquid and the solid to be milled can be circulated. The cycle is with the organic liquid filled, whereupon the solid and the grinding media are placed in the mill. Of the The cycle is closed and the mill is operated, while the organic grinding liquid and the Grist is continuously circulated through the mill. To prevent the grinding media from getting out of the Filters are provided. A container can be inserted into the circuit, which Contains grinding liquid and compensates for changes in volume during grinding.

If you want to work continuously or semi-continuously, several mills can be used one after the other be switched. Here, the product from the first mill is immediately transferred to the second mill, and so on fed to the last mill, where the end product is withdrawn. This eliminates the need for

Circulation of the material switched off. The grinding liquid can be diluted by adding further liquid take place between the mills.

The method according to the invention is particularly advantageous for the production of lubricating greases which are thickened with the oleophilic solids. In the case of agitator mills with a higher speed, e.g. B. with a Peripheral speed of 457 m / min or more it possible, in a viscous liquid, e.g. B. a Mixture of a volatile organic liquid with the lubricating oil to be thickened into a lubricating grease grind. After grinding, the volatile organic liquid can be removed, for example by evaporation removed leaving a grease, which consists of the lubricating oil thickened with the oleophilic solid To adjust the viscosity of the Milling liquid, more volatile organic liquid can be added while increasing the viscosity As an alternative or in addition, the grinding liquid increases due to the comminution of the solid the temperature of the grinding liquid can be increased to reduce the viscosity.

The viscosity of the grinding liquid becomes 85 to 1000 cP, preferably 100 to 300 cP, measured at a shear rate of 511 sec- 'at 25 ° C.

The heating of the oil can be done by the oil flowing through the circulatory system or the steel housing or both are heated.

The method according to the invention is also suitable for the production of oleophilic mixtures of graphite and metals such as lead, antimony and bismuth

The grease preferably contains 10 to 30% by weight of oleophilic graphite or metal sulfide.

Oleophilic graphite adsorbs n-dotriacontane n-heptane is preferred over n-butanol from n-dotriacontane. The degree of affinity for the adsorbed liquid can be determined by measuring the heat of adsorption.

The heat of adsorption of n-dot triacontane from n-heptane is a measure of that from the base area of the Graphite existing surface, d. H. the area created by splitting the graphite parallel to the main surface of the Graphite crystal is formed, and the heat of adsorption of n-butanol from n-heptane is a measure of the than Pole face designated area of the graphite, which is perpendicular to the main surface due to the splitting of the graphite crystals the graphite crystals is obtained. The heat of adsorption can be measured with a flow microcalorimeter can be measured as described in Chemistry and Industry of March 20, 1955, pages 482-489.

It has been found that the thickening ability of oils to greases increases with increasing ratios

the heat of adsorption of n-dotriacontane from n-heptane to the heat of adsorption of n-butanol from n-heptane, i.e. it gets better with an increasing ratio of base area to pole area. Preferably this is up Ratio of base area to pole area measured in this way 10: 1.

It has surprisingly been found that more oleophilic Graphite, made by grinding graphite in an agitator mill, is a higher one The ratio of base area to pole area therefore results in the same amount dissolved in a lubricating oil is a thicker lubricating grease than it was previously with oleophilic Graphite was obtained. Compacts produced by pressing the product by grinding in an agitator mill oleophilic graphite, have a lower abrasion through abrasive action, and through Grinding of oleophilic graphite made in an agitator mill has better reinforcing properties in Polytetrafluoroethylene.

example 1

A commercially available agitator mill is used, which is listed in> consists essentially of a cylindrical grinding chamber surrounded by a jacket through which a heated liquid can flow. A wave on which smooth disks are equally spaced are attached to each other, runs in the chamber in airtight bearings. The lower disc is perforated The slurry enters through an internal valve at the bottom and is exited through an exit at the top End removed The shaft is driven by a motor at 1500 rpm. This wave was in one closed circuit, which consisted of a pump and a storage tank. The mill had one Capacity of 7.57 l and the container a capacity of 15.141. The grinding room of the Mill was made with a blend of a base oil, a solvent refined oil with a viscosity of 160 Redwood No. 1 seconds at 60 ° C, corresponding to 38.9 centistokes and one Viscosity index of 95, and a petroleum derived paraffinic fraction boiling range 70 to 100 ° C filled.

The mill was »60% filled with the grinding media and graphite. The mill and pumps were switched on, whereupon the graphite was ground. The slurry made after a set meal was formed, was taken from the pressure side of the pump. The paraffinic fraction was derived from the Slurry evaporated to form a grease. The results are shown below in Table 1 named.

Table 1

Grinding liquid 9.75 kg oil / 11.60 kg oil / 4.20 kg par. Fract. 9.10 kg par. Fract Grinding media Zircoa Steel shot Weight of the grinding media, kg 14.64 14.94 Weight of the graphite, kg 1.72 2.042 Grinding time, hours 12th 15th Grease Resting penetration *) 340 343 Walk penetration, 60 strokes 354 347

*) Measured on scale as Vio mm and converted to full scale displays using a conversion factor of (3.41 χ penetration) +74. It has been found that this conversion factor is more precise than the conversion factor used for soap-thickened fats.

The Zircoa particles were sintered zirconia beads that had a specific gravity of 5.6 and one Particle size from 0.85 to 1.7 mm. The steel shot had a specific gravity of 7.8 and a particle size of 1 to 2 mm.

Example 2

The experiment described in Example 1 was repeated with a 70% steel ball filling, a urination rate of 15 l / hour and a grinding temperature of 2 ° C. The grinding liquid consisted of 67% lubricating oil and 33% by weight of the paraffinic fraction. During the milling the milling liquid was diluted with the mixture of oil and paraffin fraction so that the milling fluid had an initial viscosity of 150 cP at a shear rate of 511 sec. ^1,.

Example 3

The experiment described in Example 2 was repeated at a grinding temperature of 45.degree

Example 7

The experiment described in Example 6 was repeated with the difference that 0.1% by weight of one commercial high molecular weight polyethylene and 2.0 wt .-% of an atactic polypropylene, based on the final weight of the grease with which diluent was added and the exit viscosity at 200 to 270 cP at a shear rate of 511 sec- '.

Example 8

The experiment according to Example 7 was repeated with the addition of only 0.1% by weight of ues polyethylene

Example 9

The experiment according to Example 7 was repeated, but using the polymers with the last oil addition were added to the grinding liquid.

25th

Example 4

The experiment described in Example 2 was repeated with the difference that the slurry was only diluted with the paraffin fraction so that that the viscosity is 150 cP at a shear rate from 511 sec.

Example 5

The experiment described in Example 2 was repeated with the difference that the Exit viscosity from 125 cP at the start of milling to 230 cP as measured at a shear rate of 511 sec- ', at the end of the grinding.

Example 6

The experiment described in Example 2 was repeated with the difference that the outlet viscosity was ^{maintained at 220 to 250 cP at a shear rate of 511 sec-1} and only lubricating oil was added as a diluent. The paraffin fraction content in the final slurry was only 25% by weight of the milling liquid

Example 10

The following comparative experiment was carried out: A lubricating grease thickened with oleophilic graphite was produced by dispersing 15% by weight of a graphite in the lubricating oil 3G 160/95. The oleophilic graphite was produced by grinding graphite in isooctane in a vibrating ball mill. A commercially available vibrating ball mill was used as the mill. In the type used for this experiment, the grinding spaces were formed by steel cylinders with an internal diameter of 31.2 mm and a length of 381 mm. The grinding spaces were almost filled with steel balls with a diameter of 6.4 mm V ₈ PS provided. The oscillation amplitude was 4 mm. Each cylinder was completely filled with isooctane for grinding, followed by the addition of the steel balls and 25-30 grams of graphite. About 150 to 200 ml of isooctane remained in each cylinder. The ends were then closed with metal caps fitted with rubber gaskets, followed by grinding. After milling, the contents of the cylinders were placed in sieves that held back the balls. The isooctane was removed from the oleophilic graphite by rapid evaporation

The penetration values of the lubricating greases prepared according to Examples 2-10 were measured. the Results are given in Table 2. In all cases the grease contained 15% by weight of graphite.

30th

35

40

50

55

60

65

Table 2 Grinding time, Walk penetration, example hours 60 shocks 14th 330 2 14th 343 3 14th 338 4th 13th 338 5 13th 325 6th 8th 340 7th 8th 333 8th 8th 330 9 14th 361 10

As the data show, the oleophilic graphite produced according to the invention has superior fat thickening properties compared to the oleophilic graphite, which is the best known to date Process is produced, d. L, he forms with the same Graphite concentration a harder fat

Isooctane was used because it was found that it is the best and most suitable grinding liquid for this mill

Example 11

The graphite was ground in a lubricating oil in the absence of a diluent.

The experiment described in Example 1 was repeated with the difference that the grinding chamber of the mill was filled only with the lubricating oil base oil and the mill was filled to 70% with the steel balls. The milling temperature was between 125 and 135 ° C. The exit viscosity of the slurry was maintained at 280 to 300 cP with a shear rate of 511 sec- ¹ . After cooling, a grease was obtained, the properties of which are shown in Table 5 below.

Table 5 Amount of graphite worked penetration

12%

15%

391 361

12th

example

The lubricating grease produced according to Example 3 was treated with n-heptane in a Soxhlet apparatus for 2 hours

Table 3

extracted to remove all of the lubricating oil, whereupon the n-heptane was removed. The oleophilic graphite was cold-pressed with a pressure of 4.1 10 ⁸ Wm ² (Newtons / m ² ), a hard compact being formed. The compact was tested in a lubricant testing machine with a pin and disk to measure its wear and hardness.

For comparison, from that according to Example 11 The test results are given in Table 3

graphite Example 11 Example 10 Base area, mVg 70.7 150.0 Pole face, mVg 1.85 6.5 Wear, mVmkg χ 10> 2 0.8 1.2 Final pressure, N / m ² χ 10 ⁷ 2.28 1.55 Initial modules 6.09 2.59 Change in shape at break,% 4.4 5.5

As the above values show, the has a higher ratio of base area to pole area than the

the process according to the invention produced by the best previously known process

oleophilic graphite superior properties and a 25 set oleophilic graphite

Example 13

The oleophilic graphite produced according to Example 12 mixed in an ultrasonic vibrator head

was mixed with a slurry boiled from the to in Example petroleum ether, between 40 and 6O ⁰ C, and was powdered polytetrafluoroethylene. The petroleum ether and the Polyt Urafluoräthylen were with

The oleophilic graphite produced in the manner described in Example 11 was used for comparison in treated in the same manner. The results of the tests are shown in Table 4 below.

Table 4

graphite Example 11 40 Example 10 40 % By weight graphite in the composite material 20th 1.8 20th 2.5 Wear and tear, mVtnkgx 10- ¹ ^ 2.4 2 ^ 6 5.5 2.16 Final pressure, N / m ² χ 10 ' 2.55 3.34 2.70 3.01 Initial modules 433 9.5 3.87 9.4 Change in shape at break,% 143 17.1

These values show that the polytetrafluoroethylene process is used without the Graphite produced according to the invention superior 45 other properties are deteriorated. Has wear properties when used for reinforcement

Claims (3)

Patent claims: Process for the production of oleophilic graphite by grinding graphite in an organic liquid with a viscosity of 85-1000 cP, measured at a shear rate of 511 sea - ', at 25 ⁰ C, characterized in that the mixture is ground in an agitator mill. 2. The method according to claim 1, characterized in that that the viscosity during grinding by heating, diluting or adding more Grinding fluid is maintained at 100 to 300 cP. 3. Use of the oleophilic graphite obtained according to claim 1 or 2 for production of thickened lubricating oil.