DE19852203A1 - Lubricant with solid particles with a particle size below 500 nm - Google Patents

Abstract

The invention relates to a lubricant which contains solid particles that are dispersed in an organic matrix and have a mean particle size of between 1 and 500 nm. The lubricant preferably contains between 0.05 and 30 % by weight, in relation to the total formulation, of solid particles. The organic matrix is preferably selected from among native or mineral oils or fats, carboxylic acid salts with between 12 and 44 carbon atoms, waxes and organic polymers. The solid particles are preferably selected from the metal oxides, metal hydroxides, metal nitrides, metal carbides, metal phosphides, metal borides and metal sulfides and preferably have a hydrophobic coating. The above lubricants can be used to lubricate parts moving in relation to each other, as forming aid, cutting fluid and rolling oil emulsion.

Description

The invention relates to lubricants which contain nanoscale solid particles. which are dispersed in an organic matrix. The invention encompasses Lubricant for lubricating relatively moving parts such as. B. warehouse and joints, lubricants for forming processes such as pipe or Wire drawing as well as for deep drawing and cold extrusion, lubricant for the Rolling of metal strips and cooling lubricants for metal cutting Metalworking operations. Due to the presence of the nanoscale The friction between tool and workpiece becomes additional solid particles decreased. "Nanoscale" is understood to mean solid particles whose Particle size is below 500 and in particular below 100 nm.

Two surfaces and especially two metal surfaces move relatively to each other, they heat up due to friction, causing damage to the surfaces and can lead to welding processes. It is to reduce friction known to use lubricants that are usually a lubricating organic Component included. Examples are fatty acid salts (soaps), oils and fats native and of mineral origin, waxes and synthetic polymers such as for example polytetrafluoroethylene. There are also so-called Dry lubricants known, which are preferred as such, but together with uses the organic lubricants. As a rule, these are layered solids such as metal sulfides or graphite,  which develop a lubricating effect that layers of solid particles can slide relative to each other. A systematic overview of the structure of lubricants for forming is included in: Wilfried J. Bartz: "Tribology and Lubrication in Forming Technology", expert verlag, 1987, Pages 20 to 59 a.

Lubricants are optimized for their respective use. Nevertheless there is Need to further improve the lubricating effect, for example in order to Bearing and joint life increase, higher machining to achieve speeds and the service life of the tools (rollers, Drawing dies, tools for cutting, drilling and milling).

The invention relates to a lubricant in an organic matrix dispersed solid particles with an average particle size in the range of 1 contains up to 500 nm. The average particle size is preferably less than 250 nm, in particular below 100 nm and in some cases can also be below 50 nm. Solid particles that meet these criteria in terms of particle size hereinafter referred to as "nanoscale solids". The particle size is after known methods can be determined, for example with light scattering methods. The Solid particles are preferably inorganic in nature and can X-ray crystalline or X-ray amorphous.

What proportions of nanoscale solid particles the lubricant contains depends on its physical state (liquid, pasty or almost solid) and the intended purpose. In general, the task of Reduction in friction solved satisfactorily when the lubricant, based on the total formulation, about 0.05 to about 30% by weight Solid particles with an average particle size in the range from 1 to 500 nm contains.  

Depending on the application, different organic matrix come Substance groups into consideration. For example, the organic matrix be selected from oils or fats of native or mineral origin. Here are oils or fats of native origin understood as such oils or fats, which are obtained from vegetable or animal raw materials. You pose in the Rule glycerin fatty acid esters and can be synthetic after their recovery be modified. Oils and fats of mineral origin are those based on fossil raw materials such as petroleum. You can as Main components contain aliphatic hydrocarbons (e.g. paraffin oils), however, they can also be based on aromatic hydrocarbons such as for example the naphthenic mineral oils. Furthermore, the organic Matrix consist of so-called soaps, i.e. salts of saturated or unsaturated, linear or branched carboxylic acids with a carbon chain length in Range from 12 to 44 carbon atoms, as well as from the corresponding free Carboxylic acids. Carboxylic acids in the C chain length range from about 12 to about 22 are commonly referred to as fatty acids and come as a component of animal or vegetable oils and fats. By dimerization unsaturated fatty acids from this chain length range can be so-called dimer fatty acids are obtained, the C chain length range of which is about 22 ranges up to 44. By reacting fatty acids or dimer fatty acids with The corresponding soaps can be obtained from metal oxides or metal hydroxides. Oxides in particular come as the metal component for the soap formation and hydroxides of alkali and alkaline earth metals as well as of zinc and aluminum into consideration. As an organic component in lubricants continue to come Waxes and organic (usually synthetic) polymers such as Polytetrafluoroethylene into consideration.

The nanoscale solid particles in the lubricants according to the invention are preferably selected from metal oxides, metal hydroxides, metal nitrides, metal carbides, metal phosphides, metal borides and metal sulfides. For the purposes of this selection, silicon is also counted as metal, so that, for example, silicon dioxide, silicon carbide or silicon nitride can also be used. Further examples of suitable solid particles are TiN, TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , ZnO, Al ₂ O ₃ , WC, Fe ₂ P, AlOOH, MoS ₂ , LaB ₆ , hydrotalcite and others. Some of these solids are already known as components of lubricants. However, they show an improved effect if they are at least partially in the form of nanoscale particles. It is conceivable that solids present in the layer structure, such as hydrotalcite or molybdenum sulfide, can be lubricated by the layers sliding past one another within a solid particle. With geometrically rather isotropic solid particles, which may be approximately spherical or in the form of polyhedra such as cubes, octahedra or similar shapes, it is also conceivable that the improved lubricating effect is due to the fact that these particles between the surfaces sliding past each other Unroll the tool and workpiece and thereby reduce the friction.

The solid particles are preferably with a hydrophobic coating overdrawn. This makes them more dispersible in the organic matrix. This is particularly advantageous if the organic matrix is liquid, such as it for example with oils or the oil droplets of an oil-in-water emulsion Case is. In this case, sedimentation of the solid particles in the hydrophobic matrix due to the hydrophobic coating of the solid particles prevented or slowed down. In contrast, is the organic matrix pasty or approximately solid, the solid particles can not sediment, so that a hydrophobic coating is not absolutely necessary. Therefore, in one such a matrix, nanoscale solid particles are also used that are not compatible with are coated with a hydrophobic coating.

"Hydrophobic coating" means a coating that makes the solid particles water-repellent and oil-wettable. In general, such a hydrophobic coating can be achieved by covering or reacting the particle surface with substances which carry hydrophobic groups such as alkyl or alkylene groups. Such a hydrophobic coating, also of nanoscale solid particles, is known, for example, from EP-B-636 111. The methods described there can generally be used to coat the solid particles with a hydrophobic coating for the production of the lubricants according to the invention. According to the teaching of EP-B-636 111, one can generally proceed in such a way that the unmodified powder is present in the presence of at least one organic compound having a molecular weight of not more than 500 and which has at least one functional group which is present on the surface the groups present in the powder particles can react and / or interact, dispersed in water and / or an organic solvent and then the dispersant, if appropriate, completely or partially removed. The organic compounds can be selected from aliphatic, saturated or unsaturated C ₁ to C ₁₂ monocarboxylic acids, amines of the formula R ₃ -n NH _n , where n = 0, 1 or 2 and the radicals R independently of one another alkyl groups with 1 to 12, in particular 1 to 6, carbon atoms, β-dicarbonyl compounds having 4 to 12 carbon atoms, modified alcoholates and organoalkoxysilanes. The following can also be used for the hydrophobic coating: nonionic, cationic or anionic surfactants, polyethers, polyesters, polyamides and polyimides, alcohols, organic sulfonic or phosphonic acids, amino acids or oxocarboxylic acids.

In a further aspect, the invention relates to a method for lubricating parts moved relative to each other using a lubricant as above described. There are very different areas of application to be affected. An example is the lubrication of moving relative to each other metallic and / or ceramic surfaces, the sliding against each other Parts should not be changed. Examples of this are bearings or joints such as  for example ball bearings or rotating parts such as Gear or bevel gears. In these cases, it comes down to the friction between to reduce the surfaces sliding past each other, so that as possible little frictional resistance occurs, as little frictional heat as possible arises and the surfaces are damaged as little as possible to the life of the Extend components. This is usually done using greases or oils used in which also solid particles such as graphite or Molybdenum sulfide can be dispersed. Through the use of nanoscale solid particles in these greases or lubricating oils Friction further reduced, so less force to move the parts is required (energy saving) and extends the life of the components becomes.

The invention further comprises a method for shaping metallic parts using a forming agent (drawing agent), where as Forming agent uses a lubricant as described above. So here it is to processes in which the shape of a metallic workpiece in particular is changed by allowing a force to act on the workpiece. For example, cold extrusion and deep drawing are affected. Farther this aspect of the invention encompasses wire, bar or tube drawing, where the cross section or the wall thickness of the workpiece is reduced and that Workpiece itself is extended. Lubricants are often used for this, the fatty acid or fatty acid soaps such as stearic acid and stearates contain. Beef tallow is also suitable as an organic base. In the state of the It is already known in the art that such components have inorganic components such as boric acid and borates, phosphates, carbonates or silicates to add. According to the invention, nanoscale solid particles are used, which Significantly improve forming behavior. This can result in a greater reduction the cross section per drawing step, an increase in the drawing speed and / or  an extension of the tool life can be achieved. The same applies to Cold extrusion and deep drawing.

In the method according to the invention for lubricating relative to each other moving parts or for forming metallic parts using a Forming agent is preferably a lubricant that is not less than 1, preferably not less than 2, but preferably not more than about 25 and especially not more than about 20% by weight based on the total mass of the lubricant contains nanoscale solid particles.

The invention further relates to a method for machining Metalworking using a cooling lubricant, being called Cooling lubricant uses a lubricant as described above. For this use, the lubricant is preferably liquid. Such Lubricants used in metal cutting processes such as for example cutting, drilling, turning, milling, grinding, honing or lapping are usually referred to as "cooling lubricants". This expresses that these lubricants are not only for lubrication, but also for cooling, d. H. Paying off at the cutting Metalworking generated heat serve. The coolant can available exclusively as an oil phase. For this is also the term "cutting oil" known. Such cutting oils have a particularly good lubricating effect, cannot dissipate heat as efficiently as water-based ones Coolants. The cutting oil can be a paraffinic or naphthenic Represent mineral oil. However, it can also be a so-called "synthetic oil" like represent, for example, a polyolefin or an ester or ether, its molecules have at least 8 carbon atoms. Polyalkylene glycols also come Polyalkylene glycol ether or ester oils of natural origin, which may be chemical may be modified. These oils can also be called EP additives ("extreme pressure") such as phosphorus or  contain organic sulfur compounds or halogenated hydrocarbons. These improve the lubrication behavior. By dispersing nanoscale Solid particles that are preferably hydrophobic for this purpose Wear surface coating, the lubrication effect is further improved. This enables higher working speeds and a longer service life the tools are extended. This method is preferably used Cutting oil containing about 0.5 to about 20, and especially about 1 to about 10 parts by weight %, based on the total formulation, contains nanoscale solid particles.

Furthermore, the cooling lubricant used in the metal-cutting process can be an oil-in-water emulsion. The oil components that can be used are those substances that were described above as the basis of the cutting oils. Such oil-in-water emulsions, which are also referred to as "water-mixed cooling lubricants", have the advantage over the cutting oils of improved heat dissipation. When ready for use, they usually contain about 0.5 to about 3% by weight of the oil component. In addition, emulsifiers are usually required to stabilize the emulsion. In order to suppress the corrosion effect of the water phase, corrosion inhibitors such as ethanolamines or fatty acids with chain lengths of about C ₆ to about C ₁₀ are generally used.

Usually, the water-mixed cooling lubricants do not come as such, but rather as water-miscible concentrates. The concentrates contain typically about 20 to about 80% by weight, and especially about 30 to about 50% % By weight of the oil component, the remainder consisting essentially of 100% Emulsifiers, corrosion inhibitors and smaller amounts of water. These concentrates are made ready for use by dilution with water Oil-in-water emulsion. You usually use about 2 to about 10 weight percent concentrate and about 98 to about 90 weight percent water. For the  Use according to the invention contain the concentrates of the water-miscible Cooling lubricants, based on the total mass of the concentrate, preferably about 1 to about 20% by weight nanoscale solids, preferably one Have hydrophobic surface coverage. The water-diluted ready-to-use oil-in-water emulsion then contains, based on the Total mass of the emulsion, preferably about 0.05 to about 2% by weight of the nanoscale solids.

Furthermore, the invention relates to a method for rolling metal strips, the both the peculiarities of a forming process (change in shape) as well metal cutting (surface abrasion). By doing Processes for rolling metal strips are used according to the invention Rolling oil or a rolling oil emulsion, being used as rolling oil or as a rolling oil emulsion uses a lubricant as described above. You can use a substantially anhydrous single phase oil, preferably additionally contains EP additives. Rolling oils are usually on one corresponding base constructed as the cutting oils described above. If a single-phase rolling oil is used, it preferably contains nanoscale Solid particles in a proportion, based on the total mass of the Total formulation, from about 0.5 to about 20 and especially from about 1 to about 10% by weight.

In addition to a single-phase rolling oil, one can also be used to roll metal strips Rolling oil emulsion can be used, which is either an oil-in-water emulsion or represents a water-in-oil emulsion. Similar to water-miscible Cooling lubricants usually come as these anhydrous rolling oil emulsions or low-water concentrate commercially, which is the oil component, usually Contains EP additives, emulsifiers and, if necessary, corrosion inhibitors. This becomes the ready-to-use emulsion by dilution with water generated. The ready-to-use rolling oil emulsion preferably contains, based on  the total mass of the emulsion, about 0.05 to about 2 wt .-% nanoscale Solid particles, preferably a hydrophobic surface coating wear.

Embodiments

Nanoscale solids are commercially available. For example, you can are produced by reaction, for example hydrolysis, ammonolysis or Pyrolysis in the gas phase, by electrolysis or by chemical reaction in an emulsion, the size of the emulsion droplets being the size of the emerging nanoparticles limited. For the purpose of the invention preferably used nanoscale solid particles that are hydrophobic Have surface coating. This coating can be made according to one of the Processes are described which are described in EP-B-636 111. Further exemplary processes for making the hydrophobic Surface coating are:

example 1 Surface modification of nanoscale titanium nitride

98 g of TiN with an average particle size of 15 nm were used for the reaction (Supplier: H.C. Starck), 6 g 3-aminopropyltriethoxisilane and approx. 400 ml n-octane required. The titanium nitride was introduced into ethanol with the exclusion of air and stirred. The ethanol was suctioned off and the powder twice with 100 ml Washed ethanol. After that, it became dry with nitrogen sucked and used for the actual reaction. For this it was made in n-octane recorded, heated to 80 ° C and the ethanol still adhering to the TiN distilled off. To the mixture cooled to room temperature was added  The 3-aminopropyltriethoxisilane dissolved in n-octane is added with stirring. The mixture was then refluxed for 5 hours (temperature about 115 to 120 ° C), the solid is suction filtered, washed 3 times with about 100 ml of n-octane and over Dried overnight at 80 ° C in a vacuum drying cabinet.

Example 2 Hydrophobic titanium dioxide

11 g of TiO _{2 with} an average particle size of 30 nm (supplier: company Degussa), 4.3 g of palmitic acid and 165 ml of n-octane were used. The palmitic acid was dissolved in n-octane with gentle heating (40 ° C.) and the TiO _{2 was introduced} . The mixture was then heated to reflux (about 126 ° C.) and the water formed was discharged from the reaction mixture using a water separator. After 1.5 hours, the reaction mixture was allowed to cool to room temperature, the solid was isolated by centrifugation, washed with fresh n-octane, centrifuged again and dried at 90 ° C. in vacuo.

Example 3 Lubricant for wire or tube drawing

a) A basic recipe consists of

78.8% by weight of stearic acid
10.3 wt% NaOH
1.4 wt% KOH
8.6% by weight sodium tetraborate pentahydrate
0.9% by weight sodium nitrite.

The mixture is additionally mixed with 2, based on the mass of the end product up to 10% by weight of nanoscale titanium dioxide (preferably anatase).

b) A basic recipe consists of

54.0% by weight calcium hydroxide
11.0% by weight calcium sulfate dihydrate
35.0% by weight beef tallow.

The mixture is additionally with, based on the mass of the end product, 2 to 10% by weight of nanoscale titanium dioxide (preferably anatase) are added.

Example 4 Concentrate of a water-miscible coolant

The example shows a concentrate for a water-miscible cooling lubricant for use in metal cutting. The ready-to-use cooling lubricant emulsion can be obtained in the form of an oil-in-water emulsion by mixing about 2 to about 10 parts by weight of concentrate with about 98 to about 90 parts by weight of water.

Basic recipe in% by weight:

33.5 paraffinic mineral oil,
1.0 oleyl / cetyl alcohol × 10 moles of ethylene oxide,
4.0 p-hydroxybenzoic acid propyl ester,
2.0 3,5,5-trimethylhexanoic acid,
12.0 dimer fatty acid,
7.0 fatty acid mixture (main component: oleic acid),
9.0 potassium hydroxide,
18.0 oleyl / cetyl alcohol × 2 moles of ethylene oxide,
1.0 diethylene glycol monobutyl ether,
2,2 2-octyldodecyl alcohol,
10.3 ethylene glycol monophenyl ether.

The basic recipe is, based on the mass of the end product, 0.5 to 20 preferably 1 to 10 wt .-% of a nanoscale solid mixed. The nanoscale solid preferably bears a hydrophobic one Surface coating. For example, the products come according to examples 1 and 2 into consideration.

Claims (11)

1. Lubricant containing solid particles dispersed in an organic matrix contains an average particle size in the range from 1 to 500 nm. 2. Lubricant according to claim 1, characterized in that it, based on the total formulation, 0.05 to 30 wt .-% solid particles with a contains average particle size in the range of 1 to 500 nm. 3. Lubricant according to one or both of claims 1 and 2, characterized characterized in that the organic matrix is selected from oils or fats native or mineral origin, salts of carboxylic acids with a C chain length in the range of 12 to 44 carbon atoms, waxes and from organic Polymers. 4. Lubricant according to one or more of claims 1 to 3, characterized characterized in that the solid particles are selected from metal oxides, Metal hydroxides, metal nitrides, metal carbides, metal phosphides, Metal borides and metal sulfides. 5. Lubricant according to one or more of claims 1 to 4, characterized characterized in that the solid particles with a hydrophobic coating are covered. 6. A method of lubricating parts moving relative to each other, thereby characterized in that a lubricant according to one or more of the Claims 1 to 5 uses. 7. Method of forming metallic parts using a Forming agent, characterized in that a  Lubricant according to one or more of claims 1 to 5 is used. 8. Method of metal cutting using a Cooling lubricant, characterized in that one as a cooling lubricant Lubricant according to one or more of claims 1 to 5 is used. 9. The method according to claim 8, characterized in that the cooling lubricant represents a cutting oil. 10. The method according to claim 8, characterized in that the cooling lubricant represents an oil-in-water emulsion. 11. Method of rolling metal strips using a rolling oil or a rolling oil emulsion, characterized in that as rolling oil or as a rolling oil emulsion, a lubricant according to one or more of the claims up to 5.