DE202024100077U1 - Metal- and halogen-free, thermally stable solid lubricant additives - Google Patents

Abstract

Use of a compound of formula (Ia) or (Ib) AX (Ia) A ⁺ X ^- (Ib)
where A and A ⁺ represent a derivative of a 2,4,6-amine-functionalized-1,3,5-triazine or a positively charged cation thereof;
X and X ^- are selected from the group consisting of 1,3,5-triazine-2,4,6-trithiol, 1,3,5-triazine-2,4,6-tris-alkylaminocarboxylic acids or the corresponding carboxylates and polyphosphates;
as a solid lubricant for preparing a lubricant composition.

Description

Technical field of the invention

The present invention relates to thermally stable, metal- and halogen-free solid lubricants which are used as thickeners, EP/AW (extreme pressure/anti wear) additives and friction modifiers in aqueous, oil or grease applications, as coatings and as dry films.

Background of the invention

Solid lubricants, used in aqueous suspensions, oils and greases or as dry films as friction-reducing, extreme pressure and/or anti-wear additives, improve lubrication and thus the performance of the lubrication system for many different industrial applications. They smooth out surface irregularities by adhering to the substrate and separating the surfaces from each other. They effectively reduce friction in applications where the sliding parts have - microscopically speaking - rough surfaces. As EP and AW additives, they can reduce wear and welding under severe operating conditions, shock loads, vibration and frequent start-stop operations. Both at ambient temperature and at high temperatures, they are used in modern drive systems in aerospace, nuclear power plants, the automotive industry, heavy-duty industries, metal processing (cutting, forming, forging, etc.), coatings, metallurgy, etc. Ideally, solid lubricants are chemically inert to the materials used in the application.

Some solid lubricants such as polyurea, organophilic clays, fluoropolymers, etc. act as oil thickeners by increasing the viscosity of the oil.

Common solid lubricants are layered lattice solids such as graphite, graphene, transition metal dichalcogenide (e.g. MoS ₂ , WS ₂ ) and hexagonal boron nitride (h-BN), polymers such as polytetrafluoroethylene (PTFE) and polyimide, soft metals such as Pb, Ag, Au, Pt, Zn, In, Sn, Pb, chemically stable fluorides such as BaF ₂ , CaF ₂ , CeF ₃ , chromates and sulfates of alkaline earth metals. For certain applications, combinations of solid lubricants may be more suitable than single-component solid lubricants. As EP and AW additives, solid lubricants form extremely thin protective layers on the sliding surfaces of the materials. As friction modifiers, they are used to reduce friction and wear between two moving, rolling or sliding surfaces. Normally, the friction between lubricant and surface is much lower than the friction between the surfaces in an unlubricated system.

Not all solid lubricants are easily interchangeable, for example certain environmental conditions require a particular lubricant; for example, some solid lubricants work better at low temperatures but fail at high temperatures, while others require moisture to work well.

Molybdenum sulfide, graphite and PTFE are certainly the most commonly used solid lubricants as EP additives. Graphite is known to be used as a solid powder, but can also be used in lubricant compositions such as oils and greases. Graphite has a very high thermal stability. However, due to oxidation processes, practical application at high temperatures is limited to a range of max. 500 °C to 600 °C. To achieve low friction, graphite relies on the adsorption of moisture or water vapor. Its use in a dry environment, especially in a vacuum, is limited. In addition, the dark blue to black appearance of MoS ₂ and graphite limits their suitability for applications where light-colored greases are preferred.

PTFE is classified as a very efficient lubricant with a particularly low coefficient of friction despite a high wear rate due to its hydrophobicity and the dry, shiny film it forms on surfaces. It prevents the accumulation of dust and other particles that could otherwise form an abrasive paste. However, PTFE has some disadvantages: while PTFE is stable and non-toxic at lower temperatures, it begins to break down at temperatures above 260 °C and decomposes above 350 °C to form toxic fluorocarbon compounds. In addition, PTFE particles can change shape under pressure, reducing abrasion resistance. PTFE remains in the environment indefinitely and PTFE-related byproducts (perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) are known to increase the risk of certain cancers.

MoS ₂ and WS ₂ are other well-known solid lubricants that are used particularly in vacuum applications. Unlike graphite, their performance does not depend on the absorption of water or other liquids to develop lubricating properties. In contrast, the lubricity deteriorates significantly when exposed to, for example, moisture from the environment. One of the main requirements for achieving low friction of MoS ₂ is the absence of impurities such as oxygen, water and hydrocarbons. MoS ₂ is thermally stable in non-oxidizing environments up to 1100 °C. In air, however, the initial temperature of oxidation of MoS ₂ is around 350 °C. The oxidation product (MoO ₃ ) is considered abrasive. WS ₂ is a better lubricant than MoS ₂ at high temperatures both in air and in non-oxidizing atmospheres, but also begins to oxidize noticeably above 425 °C.

Less commonly used materials are soft precious metals, inorganic fluorides, and alkaline earth chromates and sulfates.

Soft precious metals such as Ag and Au offer good lubricity due to increased ductility and plastic deformation over a wide temperature range. However, the high cost limits their wide application.

CaF ₂ and BaF ₂ are chemically stable, non-layered inorganic compounds under oxidizing conditions, which have low shear strength and easy film formation; at temperatures of 500 to 900 °C they offer good lubricating properties. However, under humid and acidic conditions they release hydrogen fluoride, an extremely toxic gas that forms corrosive and transdermally active hydrofluoric acid. Alkaline earth chromates and sulfates of barium have very good thermal stability and promising lubricating properties over a wide temperature range, but also have undesirable toxicological disadvantages.

Ultimately, there is no simple one-size-fits-all solution for solid lubricants: certain properties such as the high price, the sometimes undesirable darkening of oils and greases, temperature stability, toxicological properties and negative impacts on the environment require careful consideration when selecting solid lubricants and thus limit their universal use.

The object underlying the present invention can therefore be seen in the provision of further effective solid lubricants which offer good EP/AW lubrication without impairing the friction properties (CoF) in a wide temperature range, are thermally stable under oxidative conditions and elevated temperatures, are odorless and free of halogens and metals and enable the production of colorless or white lubricant preparations with a cost-effective price-performance ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The aim of the present invention is to provide a novel solid lubricant or combinations thereof which eliminates at least one of the disadvantages of the prior art and at the same time has comparable or even better tribological properties.

in der R = H oder Alkyl in Form einer linearen oder verzweigten Kohlenwasserstoffkette, ausgewählt aus der Gruppe C_aH_b (a = 1-18, b = 3-37), darstellt, wobei das exocyclische Stickstoffatom bzw. die exocyclischen Stickstoffatome symmetrisch oder unsymmetrisch substituiert sein können, und X bzw. X^- aus der Gruppe der Verbindungen ausgewählt ist, die aus Polyphosphaten, Trithiocyanursäure oder ihrem tautomeren 1,3,5-Triazinan-2,4,6-trithion und (1,3,5-Triazin-2,4,6-triyltriimino)-trialkansäuren oder deren gemischten Carboxylaten besteht:

The inventors have surprisingly found that certain melamine adducts or salts have the ability to significantly improve extreme pressure (EP) and anti-wear (AW) properties without significantly affecting the coefficient of friction (CoF). Therefore, in a first aspect, the present invention provides solid adducts, complexes or salts of amine-functionalized 1,3,5-triazine (A or A ⁺ ) with neutralizing components (X or X ^- ) in solid form having the following composition: A-XorA ⁺ X ^- where A or A ⁺ stands for 2,4,6-triamino-1,3,5-triazine or its cationic structure, as well as for alkylated 2,4,6-triamino-1,3,5-triazine or its cationic structure,

in which R = H or alkyl in the form of a linear or branched hydrocarbon chain selected from the group C _a H _b (a = 1-18, b = 3-37), where the exocyclic nitrogen atom(s) may be symmetrically or asymmetrically substituted, and X or X ^- is selected from the group of compounds consisting of polyphosphates, trithiocyanuric acid or its tautomeric 1,3,5-triazinane-2,4,6-trithione and (1,3,5-triazine-2,4,6-triyltriimino)-trialkanoic acids or their mixed carboxylates:

The molecular ratio between A (or A ⁺ ) and X (or X ^- ) is between 1:1 and 1:1.1, preferably between 1:1 and 1:1.05 and particularly preferably between 1:1 and 1:1.01. The degree of polymerization (n) is in the range of 5-1000 units, preferably between 15-200 units and most preferably between 20-100 units.

Although the average particle size of the lubricant according to the invention is not limited to a specific range, the particle diameter D _v (95) is preferably 50 µm, more preferably D _v (95) is 20 µm, and most preferably D _v (95) is 10 µm. D _v (95) refers to the particle size distribution in which 95% of the particles are below the stated size. It is measured by laser diffraction scattering on a particle size analyzer "SYMPATEC HELOS H3641".

The present invention provides effective solid lubricants with impressive EP performance without negatively affecting the friction properties of the carrier medium. They are halogen- and metal-free, non-staining and can be used in a wide range of applications due to their light color, high temperature stability and cost-effectiveness.

In addition to other known manufacturing processes for melamine polyphosphate (MPP), for example, US7649038B2 the production of MPP from melamine phosphate, a monomelamine salt of orthophosphoric acid. Melamine phosphate is obtained by reacting melamine and phosphoric acid, dried and heat-treated at 380°C in an ammonia atmosphere. The melamine polyphosphate obtained according to the present invention can be pulverized to a desired particle size by a ball mill, a jet mill or the like.

CN104478817 describes a process for the preparation of melamine thiocyanurate (MTC) from melamine and trimercaptotriazine. Using a suitable solvent, a stirred suspension of the solid starting materials in a preferred ratio is heated at elevated temperature for several hours until all starting materials are consumed. Once the self-assembly and alignment of the newly formed units is complete, the solid is separated from the liquid layer by filtration, dried in vacuum and pulverized to the desired particle size using a ball mill, jet mill or similar.

Melamine tricarboxylates are manufactured based on the US patent US5677450 made from melamine and (1,3,5-triazine-2,4,6-triyltriimino)trialkanoic acids. An aqueous dispersion of the respective tricarboxylic acid in deionized water is added to a boiling hot, dilute solution of melamine in deionized water and the resulting mixture is stirred thoroughly. The melamine tricarboxylate salt precipitates by concentrating and then cooling the mixture. The solid is filtered off, then dried in a vacuum and pulverized to the desired particle size using a ball mill, a jet mill or similar.

Alkylated melamine phosphates, alkylated melamine thiocyanurates and alkylated melamine tricarboxylates can be prepared by those skilled in the art using the known standard procedures as for the non-alkylated melamine compounds.

The aforementioned solid lubricant can be used as a dry substance ("as is") or as a mixture of solid lubricant in a polar or non-polar, aqueous or organic carrier medium selected from a group of readily available substances such as mineral oils, synthetic oils, perfluoropolyethers, silicone oils, polyalkylene glycol, polyol esters, native or synthetic ester oils, water, glycols, silicones, silanes, acrylates or polyurethanes or mixtures and dispersions thereof.

In order to observe a measurable improvement in performance in terms of wear, high pressure, friction reducing properties in the applications, a content of the embodiment in relation to the total mass of the solid lubricant in the carrier medium preferably between 1-20 mass percent, more preferably between 1-15 mass percent and most preferably between 1-12 mass percent is required.

Production of lubricant compositions

Examples of lubricant compositions having the tribological and lubricating properties indicated in TABLE 1 are prepared, as is known to those skilled in the art, by mixing a solid lubricant or a mixture of solid lubricants with a carrier medium. A usable lubricant composition is obtained by subsequent dispersion and homogenization using a three-roll mill or alternatively using a high-pressure homogenizer.

Other additives such as antioxidants, corrosion inhibitors, viscosity improvers, etc. can be added to the composition.

Performance test

Determination of wear properties - AW

AW tests are carried out on a four-ball apparatus (Hansapress VKA-110), which consists of one rotating and three fixed balls, a drive unit and a load arm with the test weights. The material and diameter of the balls are standardized. The fixed balls are fixed in a cup. The cup is filled with the lubricant to be tested so that the fixed balls are completely covered with lubricant. The test is carried out according to DIN 51350-5 at 25 °C, a load of 150 Newton and a speed of 1450 rpm for 1 hour. After completion of the test, the diameters of the wear scars [µm] are measured. The average values of the wear cap for three balls are shown in TABLE 1.

Determination of high pressure properties - EP

EP tests are carried out on a four-ball apparatus (Hansapress VKA-110), which consists of one rotating and three fixed balls, a drive unit and a load arm with the test weights. The material and diameter of the balls are standardized. The fixed balls are fixed in a cup. The cup is filled with the lubricant to be tested so that the fixed balls are completely covered with lubricant. The test is carried out on a four-ball apparatus according to DIN 51350-4 at 25 °C, speed 1450 rpm, variable load until the welding force is reached. The average welding force (measured in [N]) was entered in TABLE 1.

Determination of the coefficient of friction - CoF

The coefficient of friction (CoF, µm) is a dimensionless scalar value that corresponds to the ratio between the frictional force between two bodies and the force that presses them together either during or at the beginning of sliding.

1. 1. Skriptparameter

a. Schwingungsamplitude: 1 µm b. Testprogramm: 50 N für 120 Sek. bei 49.5 Hz, 150 N für 60 min bei 49.5 Hz c. Temperatur: 25°C d. Probekörper: Oberer Probekörper: Kugel Ø 10 µm), 100Cr6, poliert, Unterer Probekörper: MC-proprietäre Metallplatte; 43.24 × 30.54 × 5.20 µm

• 2. Metallplatte und Kugel werden gemäß der Bruker-Anleitung in das Tribometer gespannt.
• 3. Ein kleiner Tropfen der Schmierstoffzusammensetzung wird aufgetragen.
• 4. Experiment wird gestartet.
• 5. Der Reibungskoeffizient nach der CoF-Berechnungsroutine wird berechnet und in TABELLE 1 als dimensionsloser Skalar eingetragen.

The CoF value is influenced by several factors, which is why a standardized method for determining it is necessary to achieve comparable results. The test series described here is carried out on a BRUKER UMT tribometer. The respective method can be carried out as follows:

1. 1. Script parameters

a. Vibration amplitude: 1 µm b. Test program: 50 N for 120 sec. at 49.5 Hz, 150 N for 60 min at 49.5 Hz c. Temperature: 25°C d. Test specimen: Upper specimen: ball Ø 10 µm), 100Cr6, polished, Lower specimen: MC proprietary metal plate; 43.24 × 30.54 × 5.20 µm

• 2. The metal plate and ball are clamped into the tribometer according to the Bruker instructions.
• 3. A small drop of the lubricant composition is applied.
• 4. Experiment is started.
• 5. The coefficient of friction according to the CoF calculation routine is calculated and entered in TABLE 1 as a dimensionless scalar.

Test results

TABLE 1 shows the results of AW, EP and CoF measurements for various commonly used solid lubricants in a lithium grease (NLGI grade 2, V40: 100cSt) in different concentrations from 1 to 5 weight percent.

As shown in TABLE 1, the lubricant compositions (entries 2-18) were compared with an additive-free carrier medium (entry 1) regarding their EP properties.

Using 1% MPP as a solid lubricant in a lubricant composition increases the welding force of the carrier medium by 30% from 2000 N to 2600 N, while adding 5% MPP to the carrier medium improves the welding force by 155% from 2000 N to 5100 N ( 1 ).

When using 1% MTC as a solid lubricant in a lubricant composition, the welding force of the carrier medium increases by 50% from 2000 N to 3000 N, while adding 5% MTC to the carrier medium results in an improvement in the welding force by 80% from 2000 N to 3600 N ( 2 ).

In a direct comparison of the lubricant composition according to the invention with commonly used solid lubricants of different chemical classes, the lubricant composition according to the invention shows improved lubricating properties, as in 3 If entries 2, 4, 6 and entries 7, 8, 9 are compared with comparative entries 10-18, it can be seen that the lubricant composition according to the invention has better lubricating performance with regard to the welding load properties than a lubricant composition containing MoS ₂ , PTFE or natural graphite. In particular, the lubricant compositions (entries 6, 9) in which the embodiment of the invention makes up 5 mass percent of the total lubricant composition have significantly improved welding force characteristics compared to the comparable lubricant compositions (entries 12, 15, 18).

As further shown in TABLE 1, the lubricant compositions (entries 2-18) were compared with an additive-free carrier medium (entry 1) regarding their AW properties.

When using 1% MPP as a solid lubricant in a lubricant composition (entry 2), the diameter of the wear scar of the carrier medium is reduced by approximately 11% from 340 µm to 302 µm compared to the additive-free carrier medium (entry 1), whereas the addition of 5% MPP to the carrier medium results in a lubricant composition (entry 6) that shows a reduction in the wear scar diameter by approximately 14% from 340 µm to 292 µm ( 4 ).

In a direct comparison of the AW properties of the lubricant compositions shown in TABLE 1, the lubricant compositions according to the invention show improved AW properties, when MPP is used as a solid lubricant. As in 5 As can be seen, MPP-containing lubricant compositions (entries 2, 4, 6) reduce the diameter of the wear cap even at a concentration of more than 1 %, while other comparative entries (entries 7-18) show comparable or even adverse effects.

As also shown in TABLE 1, the lubricant compositions (entries 2-18) were compared with an additive-free carrier medium (entry 1) regarding their CoF properties.

When using 1% - 5% MPP and 1% - 5% MTC as solid lubricant in a lubricant composition (entries 2-6, entries 7-9), the friction coefficient of the carrier medium was not adversely affected. The deviations of the CoF values are within the range of the measurement accuracy ( 6 ). Table 1: Test results - EP, AW and CoF number Solid lubricant Carrier medium Concentration [w/w] EP results [N] AW results [µm] CoF 1 Not Lithium grease / 2000 340 0.101 2 MPP Lithium grease 1% 2600 302 0.098 3 MPP Lithium grease 2% 2800 270 0.112 4 MPP Lithium grease 3% 4200 297 0.01 5 MPP Lithium grease 4% 4700 298 0.119 6 MPP Lithium grease 5% 5100 292 0.113 7 MTC Lithium grease 1% 3000 401 0.109 8th MTC Lithium grease 3% 3000 490 0.113 9 MTC Lithium grease 5% 3600 531 0.117 10 _MoS2 Lithium grease 1% 2000 420 0.097 11 _MoS2 Lithium grease 3% 2200 410 0.117 12 _MoS2 Lithium grease 5% 2200 415 0.119 13 PTFE Lithium grease 1% 2000 317 0.126 14 PTFE Lithium grease 3% 2200 414 0.106 15 PTFE Lithium grease 5% 2000 381 0.096 16 NG Lithium grease 1% 2200 374 0.117 17 NG Lithium grease 3% 2400 395 0.128 18 NG Lithium grease 5% 2400 451 0.130 MPP = melamine polyphosphate; MTC = melamine thiocyanurate; MoS ₂ = molybdenum sulfide; PTFE = polytetrafluoroethylene; NG = natural graphite

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely to provide the reader with better information. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• US 7649038 B2 [0019]
• CN104478817 [0020]
• US5677450 [0021]

Claims (16)

Use of a compound of formula (Ia) or (Ib) AX (Ia) A ⁺ X ^- (Ib) where A and A ⁺ represent a derivative of a 2,4,6-amine-functionalized-1,3,5-triazine or a positively charged cation thereof; X and X ^- are selected from the group consisting of 1,3,5-triazine-2,4,6-trithiol, 1,3,5-triazine-2,4,6-tris-alkylaminocarboxylic acids or the corresponding carboxylates and polyphosphates; as a solid lubricant for producing a lubricant composition. Use according to Claim 1 , where A is the formula

wherein each R is independently selected from hydrogen and C ₁ -C ₁₈ alkyl. Use according to Claim 2 , where R is hydrogen. Use in accordance with any of the Claims 1 - 3 , where X or X- is the formula

, where n is a number between 1 and 1000. Use in accordance with any of the Claims 1 - 4 , where X represents a 1,3,5-triazine-2,4,6-tris-alkylaminocarboxylic acid and the group between the exocyclic amine function and the carboxylic acid consists of a C1-C5 alkyl chain.

Use in accordance with any of the Claims 1 - 4 , where X is a polyphosphate having a degree of polymerization (n) in the range of 5 - 1000, preferably 5 - 500 units, more preferably between 15 - 200 units and most preferably between 20 - 100 units

Use in accordance with any of the Claims 1 - 4 , where X is

stands. Use in accordance with any of the Claims 1 - 7 , wherein the molecular ratio between A and X (or A ⁺ and X ^- ) is between 1:1 and 1: 1.1, preferably between 1:1 and 1: 1.05, and most preferably between 1:1 and 1: 1.01. Use in accordance with any of the Claims 1 - 8th , wherein the compound of formula (Ia, Ib) has a particle size distribution with D _v (95) = 50 µm, preferably with D _v (95) = 20 µm, more preferably with D _v (95) = 10 µm. Use in accordance with any of the Claims 1 - 9 , comprising mixing compound Ia or Ib with a carrier medium to obtain a lubricant composition. Use according to Claim 10 , wherein the carrier medium is selected from the group of compounds consisting of base oils such as mineral oil, synthetic oils such as PAO, perfluoropolyethers, silicone oils, PAG, polyol esters, natural and synthetic ester oils, water, glycols, silicones, silanes, acrylate dispersions and polyurethane dispersions or mixtures thereof. Use in accordance with any of the Claims 10 - 11 wherein the concentration of the compound of formula (Ia, Ib) in the lubricant composition is from about 1% to about 100%, the remainder being made up by the carrier medium and other additives; preferably the concentration of the compound of formula (Ia, Ib) is in the range of about 1% to about 60%, more preferably in the range of about 1% to about 20%, and most preferably in the range of about 1% to about 12%. Use in accordance with any of the Claims 10 - 12 , wherein the lubricant composition is in the form of a lubricant paste, a lubricant wax, an anti-friction coating, a grease, a lubricating oil, a spray, a release agent, or a polishing agent. A lubricant composition comprising - a compound of formula (Ia) or (Ib) AX (Ia) A ⁺ X ^- (Ib), - where A and A ⁺ stand for a derivative of a 2,4,6-amine-functionalized-1,3,5-triazine or for a positively charged cation thereof; X and X ^- are selected from the group consisting of 1,3,5-triazine-2,4,6-trithiol, 1,3,5-triazine-2,4,6-tris-alkylaminocarboxylic acids or the corresponding carboxylates and polyphosphates, a carrier medium selected from the group of compounds consisting of base oils, such as mineral oil, synthetic oils, such as PAO, perfluoropolyethers, silicone oils, PAG, polyol esters, natural and synthetic ester oils, water, glycols, silicones, silanes, acrylate dispersions and polyurethane dispersions or mixtures thereof. Lubricant composition according to Claim 14 , where A or A ⁺ has the formula

wherein R is independently selected from hydrogen and C ₁ -C ₁₈ alkyl and wherein X or X ^- has the formula

where n is a number between 1 and 1000. Lubricant composition according to Claim 14 or 15 , where X is

stands.