LUBRICATING GREASE COMPOSITION

Abstract

The present invention relates to lubricating grease compositions comprising (a) at least one high-viscosity fluorinated oil having a viscosity of 500 to 1500 mm.sup.2/s, (b) boron nitride and (c) a binder selected from bentonite, alkali metal phosphates, aluminum phosphates, alkali metal silicates, alkaline earth metal silicates, aluminum silicates, alkaline earth metal carbonates, calcium borate, silicon dioxide, titanium dioxide, aluminum oxide and mixtures thereof. The lubricating grease compositions find use especially in the high-temperature sector, for example for the lubrication of oven pullout rails.

Claims

1. A lubricating grease composition comprising (a) at least one fluorinated oil having a viscosity of 500 to 1500 mm.sup.2/s at 40 C.; (b) boron nitride and (c) at least one binder selected from bentonite, alkali metal phosphates, aluminum phosphates, alkali metal silicates, alkaline earth metal silicates, aluminum silicates, alkaline earth metal carbonates, calcium borate, silicon dioxide, titanium dioxide, aluminum oxide and mixtures thereof.

2. The lubricating grease composition as claimed in claim 1, comprising, based in each case on the total weight of the composition, (a) 50-96% by weight of the fluorinated oil; (b) 0.9-20% by weight of boron nitride; and (c) 3-25% by weight of the binder.

3. The lubricating grease composition as claimed in claim 1 or 2, wherein the fluorinated oil has with a viscosity of 500 to 1100 mm.sup.2/s at 40 C.

4. The lubricating grease composition as claimed in any of the preceding claims, wherein the fluorinated oil is selected from perfluorinated polyalkyl ether oils, perfluorinated silicone oils and mixtures thereof, and is especially selected from perfluorinated polyalkyl ether oils and mixtures thereof.

5. The lubricating grease composition as claimed in any of the preceding claims, wherein the binder is selected from bentonite, fumed silica (SiO.sub.2), talc (magnesium silicate hydrate), calcium carbonate, calcium borate, pyrogenic titanium dioxide, aluminum oxide and mixtures thereof.

6. The lubricating grease composition as claimed in any of the preceding claims, wherein the binder is organically modified bentonite or a mixture of organically modified bentonite with at least one further binder selected from alkali metal phosphates, aluminum phosphates, alkali metal silicates, alkaline earth metal silicates, aluminum silicates, alkaline earth metal carbonates, silicon dioxide, titanium dioxide, aluminum oxide and mixtures thereof.

7. The lubricating grease composition as claimed in any of the preceding claims, wherein the boron nitride is hexagonal boron nitride, especially hexagonal -boron nitride.

8. The lubricating grease composition as claimed in any of the preceding claims, comprising essentially no PTFE.

9. The lubricating grease composition as claimed in any of the preceding claims, comprising essentially no ionic liquid.

10. The lubricating grease composition as claimed in any of the preceding claims, comprising essentially no graphite.

11. The lubricating grease composition as claimed in any of the preceding claims, additionally comprising at least one nonfluorinated oil.

12. The lubricating grease composition as claimed in any of the preceding claims, additionally comprising 0.01% to 1% by weight of water, based on the total weight of the composition.

13. The lubricating grease composition as claimed in any of the preceding claims, additionally comprising at least one additive.

14. The lubricating grease composition as claimed in claim 13, wherein the additive is selected from antioxidants, viscosity index improvers, pour point depressants, antiwear additives, anticorrosives, rust preventers, dyes, and solid lubricants.

15. The lubricating grease composition as claimed in claim 14, comprising 0.05-5% by weight of at least one additive.

16. The use of a lubricating grease composition as claimed any of claims 1 to 15 for lubrication within the temperature range from 30 C. to 700 C., especially +100 C. to 310 C.

17. The use of a lubricating grease composition as claimed in any of claims 1 to 15 for the lubrication of sliding guides and running wheels in oven systems or roller and slide bearings in driers, electric motors or ventilators, for the lubrication of molds, especially molds for the injection molding of plastics, machines and installations, especially for the food and animal feed industry.

18. A lubricating method wherein a lubricating grease composition as claimed in any of claims 1 to 15 is applied to the parts to be lubricated.

19. The lubricating method as claimed in claim 18, wherein the lubricating grease composition is applied within the temperature range from 30 C. to 700 C., especially +100 C. to 310 C.

20. The lubricating method as claimed in claim 18 or 19 for lubrication of sliding guides and running wheels in oven systems or roller and slide bearings in driers, electric motors or ventilators, for lubrication of molds, especially molds for the injection molding of plastics, machines and installations, especially for the food and animal feed industry.

Description

EXAMPLE 1

[0094] Two perfluorinated polyether oils (68% by weight of PFPE oil 1, 500 cSt at 40 C. from DuPont, USA and 10% by weight of PFPE oil 2, 1005 cSt at 40 C. from DuPont, USA) were introduced into a mixing vessel and heated to 100 C. while stirring for 15 min. Thereafter, BARAGEL (14.9% by weight, organically hydrophobically modified bentonite from Elementis Specialties Inc., USA) were introduced into the mixing vessel, the heating was switched off and the resulting mixture was stirred for five minutes. Then 0.1% by weight of water was added and the mixture was stirred for 30 min. After cooling to room temperature, boron nitride (5% by weight Boronid, ESK Ceramics GmbH & Co. KG, Germany) and an anticorrosive (2% by weight, Irgacor, BASF SE, Germany) were introduced into the mixing vessel and the resulting mixture was stirred for 30 min. The resulting lubricant grease was homogenized with a roll mill. The figures in % by weight are each based on the total weight of the lubricant grease.

[0095] Test Program and Results

[0096] The lubricating grease composition produced according to example 1 was first subjected to a VKA test (four-ball apparatus, ASTM D1831/DIN 51350-4). The VKA welding force was determined as 4800 N and the VKA wear as 0.9 mm under a load of 150 kg/1 min.

[0097] For the lubricating grease composition produced according to example 1, the thermal stability was also determined at 300 C. A measure employed for the thermal stability was the evaporation rate with time:

[0098] Hours: 0 24 72 140

[0099] Evaporation rate [%]: 0 14 26 41

[0100] In addition, the following were determined for the lubricating grease composition produced according to example 1: [0101] steel corrosion (Emcor) in distilled water (ISO 11007): grade 1/1 [0102] base oil viscosity at 40 C. (DIN 51562): 575 mm.sup.2/s and [0103] NLGI consistency class (DIN 51818): NLGI 1.

[0104] Washout Tests

[0105] Washout tests were conducted for the lubricating grease composition produced according to example 1 and three comparative samples (comparative example 1, comparative example 2, comparative example 3). For this purpose, the various samples were applied to oven pullout rails and subjected to the following cycle: the oven pullout rails were subjected to a temperature of 250 C. in an oven for 4 h; thereafter, the rails were taken out of the oven and treated with a commercial dishwashing composition in a machine dishwasher at 70 C. for 2 h; after the wash cycle, the rails were taken out of the machine dishwasher and dried at 105 C. for 1 h. (3 cycles were conducted for each sample; the rails were thus in the oven for a total of 12 h and in the dishwasher for 6 h.) Composition of the comparative examples (% by weight, based on the total weight of the composition):

COMPARATIVE EXAMPLE 1

[0106] 74.75% PFPE (perfluorinated polyether; 500 mm.sup.2/s)

[0107] 25% PTFE (polytetrafluoroethylene)

[0108] 0.25% anticorrosive

COMPARATIVE EXAMPLE 2

[0109] 81% PFPE (500 mm.sup.2/s)

[0110] 10% PFPE (1005 mm.sup.2/s)

[0111] 5% PTFE

[0112] 2% SiO2

[0113] 2% anticorrosive

COMPARATIVE EXAMPLE 3

[0114] 10% PFPE (1005 mm.sup.2/s)

[0115] 83% PFPE (500 mm.sup.2/s)

[0116] 5% boron nitride

[0117] 1% graphite

[0118] 1% WS.sub.2 (tungsten sulfide)

[0119] The following results were obtained: [0120] Example 1: weight loss after the third wash cycle: <50%; rail has good mobility. [0121] Comparative example 1: weight loss after the third wash cycle: 75% [0122] Comparative example 2: weight loss after the third wash cycle: 50% [0123] Comparative example 3: weight loss after the third wash cycle: 60% [0124] Comparative example 2, which contains PTFE, evolves toxic, vaporous breakdown products and is therefore unsuitable for use in baking ovens in spite of good washout results.

[0125] Endurance Tests

[0126] Endurance tests were conducted for the lubricating grease composition produced according to example 1 and two comparative samples (comparative examples 4 and 5). For this purpose, the various samples were applied to oven pullout rails and the pullout rails were mounted on side grids. Subsequently, the grids were installed into a baking oven. A test load was positioned in the middle of a baking sheet in the oven. The weighted baking sheet was pulled in and out using a pneumatic cylinder. The rails were subjected to an endurance test with 24 000 cycles. After every 6000 cycles, movement force and lowering of the rails were tested and, likewise after every 6000 cycles, the rails were subjected to a machine dishwasher wash cycle. After a total of 24 000 cycles, the rails were deinstalled and examined. The testing was conducted with the following parameters and according to the following schematic procedure:

TABLE-US-00001 Test Cycles: 24 000 parameters: Additional load: 7.5 kg Temperature: 250 C. Speed: 10 cycles/min Level: middle level in the baking oven Pullout: restriction by 20 mm in both directions Test 1. Installation of the rails procedure: 2. Application of the test load in the middle of the baking sheet 3. Endurance test for 24 000 cycles 4. Determination of the movement force and lowering after every 6000 cycles 5. Machine dishwasher cycle after every 6000 cycles 6. Deinstallation and examination of the rails 7. Evaluation

[0127] Composition of the comparative examples (% by weight, based on the total weight of the composition):

COMPARATIVE EXAMPLE 4

[0128] as comparative example 2, see above.

COMPARATIVE EXAMPLE 5

[0129] 90.5% PFPE (500 mm.sup.2/s)

[0130] 6% boron nitride

[0131] 3.25% SiO.sub.2

[0132] 0.25% anticorrosive

[0133] The following results were obtained: [0134] Example 1: The sample passed the test (5 wash cycles, good running properties up to 18 000 cycles, continuing with somewhat poorer running properties up to 24 000 cycles). [0135] Comparative example 4: The sample passed the test (5 wash cycles, good running properties up to 18 000 cycles, continuing with poorer running properties up to 24 000). However, the composition evolved toxic breakdown products at temperatures above 250 C. [0136] Comparative example 5: The sample failed the test (failed after 12 000 cycles, ball bearings jammed owing to lack of lubrication).