Perfluoropolyether lubricating grease with high colloid stability and preparation method thereof

Abstract

The invention discloses perfluoropolyether lubricating grease with high colloid stability and a preparation method thereof.The preparation method comprises the following steps that polytetrafluoroethylene micro powder and a diluent are added into a reaction kettle and stirred, a suspension is obtained, and the diluent is a fluorine-containing solvent; and adding perfluoropolyether base oil into the suspension, stirring to obtain a mixture, removing the diluent in the mixture, and degassing to obtain the perfluoropolyether lubricating grease. The perfluoropolyether is used as the base oil, the polytetrafluoroethylene micro powder is used as the thickening agent, and the diluting agent is added in the preparation process, so that the thickening agent is uniformly dispersed in the perfluoropolyether base oil, the thickening agent and the base oil are in full contact, the action area is increased, and the colloid stability of the lubricating grease is improved. The preparation process is simple, and the diluent can be removed and recycled subsequently, so that the diluent can be recycled, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lubricating grease, and in particular to a perfluoropolyether lubricating grease with high colloid stability and a preparation method thereof. Background Art

[0002] Perfluoropolyether grease generally refers to a type of special grease made from perfluoropolyether (PFPE) base oil thickened with fluorinated polymer micropowder such as polytetrafluoroethylene (PTFE). Both PTFE and PFPE are inert polymers with properties such as heat resistance, oxidation resistance, radiation resistance, corrosion resistance, and non-flammability. Therefore, perfluoropolyether grease has excellent thermal stability, chemical inertness, radiation resistance, low saturated vapor pressure, good lubricity, etc.

[0003] Different from the preparation process of soap-based grease, the preparation of perfluoropolyether grease generally directly uses finished PTFE micropowder as a thickener, which is dispersed in PFPE lubricant by blending. However, the grease samples prepared by the ordinary mixing process have uneven texture, and the comprehensive performance cannot meet the application requirements. It is usually necessary to use equipment such as a three-roll mill to finely process the crude grease sample to reduce the size of the micropowder and homogenize it. The disadvantage of this method is that the process is cumbersome and the operating conditions are high. For example, the speed and roller gap of the three-roll mill need to be carefully checked to ensure the reproducibility of each batch of products. In addition, PTFE thickened grease is achieved by physical adsorption of base oil, but the molecular force between PTFE and PFPE is weak and the thickening ability is poor. Compared with other types of grease, perfluoropolyether grease requires more thickener to prepare and form, and its colloid stability is poor and it is easy to separate oil.

[0004] The performance of perfluoropolyether grease can be improved to a certain extent by modifying the thickener, but the process is complicated. Adding specific additives is another way to improve the colloid stability of perfluoropolyether grease.

[0005] Patent document CN111100724A discloses a perfluoropolyether grease and a preparation method thereof. The perfluoropolyether grease contains the following components based on the weight of the perfluoropolyether grease: 50-95% of a lubricating base oil, 1-49.9% of a polytetrafluoroethylene thickener and 0.1-30% of a colloid modifier, wherein the colloid modifier is a fluorinated carboxylic acid and / or a fluorinated carboxylate.

[0006] Patent document CN114045185A discloses a perfluoropolyether grease and a preparation method thereof, wherein the perfluoropolyether grease comprises the following components in weight percentage: 50-80% perfluoropolyether oil, 5-40% polytetrafluoroethylene powder, 1-10% zeolite and 0.1-5% additive. The invention has high temperature colloid stability through the combined action of perfluoropolyether oil, mixed polytetrafluoroethylene powder thickener and colloid improver zeolite.

[0007] Although the above-mentioned prior art improves the colloidal stability of perfluoropolyether grease by adding one or more additives, the preparation process still requires tedious finishing treatment, with many influencing factors, which can easily cause unstable product quality. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing a perfluoropolyether grease, so as to solve the problems of poor high-temperature colloid stability and high requirements on operating conditions in the existing perfluoropolyether grease.

[0009] A method for preparing a perfluoropolyether grease with high colloid stability comprises the following steps:

[0010] (1) adding polytetrafluoroethylene powder and a diluent into a reaction kettle and stirring to obtain a suspension, wherein the diluent is a fluorine-containing solvent;

[0011] (2) adding perfluoropolyether base oil to the suspension, stirring to obtain a mixture, removing the diluent in the mixture, degassing, and obtaining the perfluoropolyether grease.

[0012] The present invention uses perfluoropolyether as base oil and polytetrafluoroethylene powder as thickener, and improves the colloidal stability of the grease by adding a diluent in the preparation process. The basic principle is to use the diluent to evenly disperse the polytetrafluoroethylene powder in the perfluoropolyether base oil, so that the thickener and the base oil are fully in contact, the effective area is increased, and the colloidal stability of the grease is improved. Subsequently, the diluent is removed and recovered to achieve the recycling of the diluent and reduce the production cost.

[0013] The diluent of the present invention uses a fluorinated solvent, which has a similar chemical composition to polytetrafluoroethylene and can better wet and disperse polytetrafluoroethylene powder to reduce agglomeration; in addition, the fluorinated solvent can dissolve perfluoropolyether oil, making the perfluoropolyether molecular chain segment more stretched, enhancing the interaction with polytetrafluoroethylene, making the polytetrafluoroethylene powder more evenly dispersed in the perfluoropolyether base oil, and thus making the subsequently prepared grease have excellent high-temperature colloid stability.

[0014] Preferably, the particle size of the polytetrafluoroethylene powder is 0.1 to 200 μm, preferably 1 to 15 μm.

[0015] Preferably, the fluorinated solvent is any one of perfluorooctane, perfluoroheptane, hexafluoropropylene dimer, hexafluoropropylene trimer, hexafluoroisopropanol, perfluorobutyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, perfluorobutyl tetrahydrofuran, and hexafluorobenzene, or a combination of two or more thereof. These diluents have a moderate boiling point and are similar in chemical composition to polytetrafluoroethylene and perfluoropolyether, and can act as a medium to increase the wettability of perfluoropolyether oil to polytetrafluoroethylene micropowder. More preferably, the fluorinated solvent is perfluorooctane, hexafluoropropylene trimer, or perfluorobutyl tetrahydrofuran.

[0016] Preferably, the mass ratio m of the polytetrafluoroethylene powder to the fluorinated solvent satisfies: 0.1≤m<1. This mass ratio allows the polytetrafluoroethylene powder to be fully dispersed while avoiding the problem of additional separation costs caused by excessive solvent. Further preferably, the mass ratio m of the polytetrafluoroethylene powder to the fluorinated solvent satisfies: 0.3≤m≤0.5.

[0017] Preferably, the kinematic viscosity of the perfluoropolyether base oil at 20°C is 20 to 4000 mm 2 / s, preferably 100 to 1500 mm 2 / s.

[0018] Preferably, the mass ratio of the polytetrafluoroethylene micropowder to the perfluoropolyether base oil is 20-30:65-80.

[0019] Preferably, in step (2), the stirring temperature is 60-120° C., the stirring speed is 100-2000 rpm, and the stirring time is 1-4 h.

[0020] Preferably, in step (2), the diluent in the mixture is removed by vacuum distillation, the temperature of the vacuum distillation is 40 to 90° C., and the vacuum degree is 10 to 10000 Pa.

[0021] Preferably, the degassing is vacuum degassing, and the vacuum degassing temperature is 50-100°C.

[0022] More preferably, the fluorinated solvent is hexafluoropropylene trimer, and the mass ratio of the hexafluoropropylene trimer to polytetrafluoroethylene powder and perfluoropolyether oil is 6 to 10:4:6 to 12. The perfluoropolyether grease prepared under this condition has better performance, with a dropping point above 187°C, a steel mesh oil separation of less than 1.6% at 100°C and 30h, and a steel mesh oil separation of less than 12.5% ​​at 250°C and 24h.

[0023] The present invention also provides a perfluoropolyether lubricating grease prepared by the above preparation method. The perfluoropolyether lubricating grease of the present invention has high colloid stability and has the advantages of reducing oil separation and extending service life when used under high temperature conditions.

[0024] Preferably, the dropping point of the perfluoropolyether grease is above 175°C; the oil separation of the steel mesh is below 2.5% at 100°C for 30 hours, and the oil separation of the steel mesh is below 15.7% at 250°C for 24 hours.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] (1) The present invention adds a diluent during the preparation process to allow the thickener and the base oil to fully contact, thereby increasing the effective area and improving the high-temperature colloid stability of the grease.

[0027] (2) The diluent of the present invention is a fluorinated solvent, which has a similar chemical composition to polytetrafluoroethylene and can better wet and disperse polytetrafluoroethylene powder to reduce agglomeration. At the same time, the fluorinated solvent can dissolve perfluoropolyether oil, making the perfluoropolyether molecular chain segments more stretched, enhancing the interaction with polytetrafluoroethylene, and making the polytetrafluoroethylene powder more evenly dispersed in the perfluoropolyether base oil, thereby making the subsequently prepared grease have excellent high-temperature colloid stability.

[0028] (3) The formula and process of the present invention are simple and easy to operate. There is no need to modify the thickener or add specific additives to increase the dropping point of the perfluoropolyether grease product and improve the colloid stability, which is beneficial for the use of the grease under high temperature conditions, reduces oil separation, and prolongs the service life.

[0029] (4) The method for preparing the perfluoropolyether grease of the present invention alleviates the disadvantages associated with the grease preparation technology, in particular, it does not rely on finishing by a three-roll mill, which is more advantageous from an industrial point of view and greatly simplifies the production process. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with embodiments.

[0031] Example 1

[0032] Add 200g of polytetrafluoroethylene powder A (PTFE, particle size 3μm) and 300g of hexafluoropropylene trimer (boiling point 110-115°C) into the reactor, stir at 25°C and 200rpm to form a white suspension, then add 450g of perfluoropolyether oil (20°C kinematic viscosity 822mm 2 / s), stirred, heated to 60°C and maintained for 30 minutes, and then stirred at 400rpm for 1 hour. After the reaction, cooled to room temperature, then turned on the vacuum pump, maintained the vacuum degree at 3000pa, raised the temperature to 70°C, removed and recovered the hexafluoropropylene trimer by reduced pressure evaporation, heated to 75°C, and vacuum degassed for 1 hour to obtain a perfluoropolyether grease with high colloidal stability.

[0033] Example 2

[0034] Add 200g of polytetrafluoroethylene powder B (PTFE, particle size 5μm) and 400g of hexafluoropropylene trimer (boiling point 110-115°C) into the reactor, stir at 25°C and 200rpm to form a white suspension, then add 450g of perfluoropolyether oil (20°C kinematic viscosity 822mm 2 / s), stirred, heated to 70°C and maintained for 30 minutes, and then stirred at 450rpm for 2 hours. After the reaction, cooled to room temperature, then turned on the vacuum pump, maintained at a vacuum degree of 3000pa, raised the temperature to 70°C, removed and recovered the hexafluoropropylene trimer by reduced pressure evaporation, heated to 75°C, and vacuum degassed for 1 hour to obtain a perfluoropolyether grease with high colloidal stability.

[0035] Example 3

[0036] Add 200g of polytetrafluoroethylene powder C (PTFE, particle size 8μm) and 500g of hexafluoropropylene trimer (boiling point 110-115°C) into the reactor, stir at 25°C and 200rpm to form a white suspension, then add 450g of perfluoropolyether oil (20°C kinematic viscosity 822mm 2 / s), stirred, heated to 80°C and maintained for 30 minutes, and then stirred at 500rpm for 3 hours. After the reaction, it was cooled to room temperature, and then the vacuum pump was turned on to maintain the vacuum degree at 3000pa, and the temperature was raised to 70°C, and the hexafluoropropylene trimer was removed and recovered by reduced pressure evaporation, heated to 75°C, and vacuum degassed for 1 hour to obtain a perfluoropolyether grease with high colloidal stability.

[0037] Example 4

[0038] Add 200g of polytetrafluoroethylene powder B (PTFE, particle size 5μm) and 400g of hexafluoropropylene trimer (boiling point 110-115°C) into the reactor, stir at 25°C and 200rpm to form a white suspension, then add 450g of perfluoropolyether oil (20°C kinematic viscosity 450mm 2 / s), stirred, heated to 60°C and maintained for 30 minutes, and then stirred at 450rpm for 2 hours. After the reaction, cooled to room temperature, then turned on the vacuum pump, maintained at a vacuum degree of 3000pa, raised the temperature to 70°C, removed and recovered the hexafluoropropylene trimer by reduced pressure evaporation, heated to 75°C, and vacuum degassed for 1 hour to obtain a perfluoropolyether grease with high colloidal stability.

[0039] Example 5

[0040] 200 g of polytetrafluoroethylene powder B (PTFE, particle size 5 μm) and 450 g of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (boiling point 56°C) were added to the reactor, and stirred at 25°C and 200 rpm to form a white suspension. Then 450 g of perfluoropolyether oil (20°C kinematic viscosity 822 mm 2 / s), stirred, heated to 50°C and maintained for 30 minutes, and then stirred at 450rpm for 2 hours. After the reaction, cooled to room temperature, then turned on the vacuum pump, maintained at a vacuum degree of 5000Pa, raised the temperature to 60°C, removed and recovered 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether by reduced pressure evaporation, heated to 75°C, and vacuum degassed for 1 hour to obtain a perfluoropolyether grease with high colloidal stability.

[0041] Example 6

[0042] Add 200g of polytetrafluoroethylene powder B (PTFE, particle size 5μm) and 450g of perfluorooctane (boiling point 103-106°C) into the reactor, stir at 25°C and 200rpm to form a white suspension, then add 450g of perfluoropolyether oil (20°C kinematic viscosity 822mm 2 / s), stirred, heated to 60°C and maintained for 30 minutes, and then stirred at 450rpm for 2 hours. After the reaction, cooled to room temperature, then turned on the vacuum pump, maintained the vacuum degree at 3000Pa, raised the temperature to 70°C, removed and recovered the perfluorooctane by reduced pressure evaporation, heated to 75°C, and vacuum degassed for 1 hour to obtain a perfluoropolyether grease with high colloidal stability.

[0043] Comparative Example 1

[0044] Add 450 g of perfluoropolyether oil (kinematic viscosity at 20 ° C is 822 mm 2 / s) and 200g of polytetrafluoroethylene powder A (PTFE, particle size of 3μm) were added, stirred, heated to 60°C and maintained for 30min, then stirred at 400rpm for 1h, cooled to room temperature, ground with a three-roll mill for 4 times, and then vacuum degassed at 75°C for 1h to obtain a homogenous white grease.

[0045] Comparative Example 2

[0046] Add 450 g of perfluoropolyether oil (kinematic viscosity at 20 ° C is 822 mm 2 / s) and 200g of polytetrafluoroethylene powder B (PTFE, particle size of 5μm), stirred, heated to 70℃ and maintained for 30min, then stirred at 450rpm for 2h, cooled to room temperature, ground with a three-roll mill for 4 times, and then vacuum degassed at 75℃ for 1h to obtain a homogenous white grease.

[0047] Comparative Example 3

[0048] Add 450 g of perfluoropolyether oil (kinematic viscosity at 20 ° C is 822 mm 2 / s) and 200g of polytetrafluoroethylene powder C (PTFE, particle size of 8μm) were added, stirred, heated to 80°C and maintained for 30min, then stirred at 500rpm for 3h, cooled to room temperature, ground with a three-roll mill for 4 times, and then vacuum degassed at 75°C for 1h to obtain a homogenous white grease.

[0049] Comparative Example 4

[0050] Add 450 g of perfluoropolyether oil (kinematic viscosity at 20 ° C is 450 mm 2 / s) and 200g of polytetrafluoroethylene powder B (PTFE, particle size of 5μm), stirred, heated to 60℃ and maintained for 30min, then stirred at 450rpm for 2h, cooled to room temperature, ground with a three-roll grinder for 4 times, and then vacuum degassed at 75℃ for 1h to obtain a homogenous white grease.

[0051] It can be seen from Table 1 that the steel mesh oil separation of the perfluoropolyether grease prepared in the embodiment of the present invention is significantly lower than that of the grease prepared by the traditional process, indicating that the preparation method of the present invention can improve the colloidal stability of the grease. At the same time, the dropping point of the prepared grease is also improved, indicating that it has excellent high-temperature stability, a longer service life, and can be used in high-temperature environments and working conditions.

[0052] The above are preferred embodiments of the present invention. However, the present invention is not limited to the above implementation modes and embodiments. Any adjustment or modification based on the technical idea of ​​the present invention should be within the protection scope of the present invention.

[0053] Table 1 Physical and chemical properties of perfluoropolyether greases prepared in the examples of the present invention and the comparative examples

[0054]

Claims

1. A method for preparing a perfluoropolyether grease with high colloid stability, characterized in that: The following steps are involved: (1) adding polytetrafluoroethylene powder and a diluent into a reaction kettle and stirring to obtain a suspension, wherein the diluent is a fluorine-containing solvent; (2) adding perfluoropolyether base oil to the suspension, stirring to obtain a mixture, removing the diluent in the mixture, degassing, and obtaining the perfluoropolyether grease.

2. The preparation method according to claim 1, characterized in that: The particle size of the polytetrafluoroethylene powder is 0.1-200 μm.

3. The preparation method according to claim 1, characterized in that: The fluorine-containing solvent is any one of perfluorooctane, perfluoroheptane, hexafluoropropylene dimer, hexafluoropropylene trimer, hexafluoroisopropanol, perfluorobutyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, perfluorobutyltetrahydrofuran, and hexafluorobenzene, or a combination of two or more thereof.

4. The preparation method according to claim 1, characterized in that: The mass ratio m of the polytetrafluoroethylene powder to the diluent satisfies: 0.1≤m<1.

5. The preparation method according to claim 1, characterized in that: The kinematic viscosity of the perfluoropolyether base oil at 20°C is 20 to 4000 mm 2 / s.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the polytetrafluoroethylene micropowder to the perfluoropolyether base oil is 20-30:65-80.

7. The preparation method according to claim 1, characterized in that: In step (2), the stirring temperature is 60-120° C., the stirring speed is 100-2000 rpm, and the stirring time is 1-4 h.

8. The preparation method according to claim 1, characterized in that: In step (2), the diluent in the mixture is removed by vacuum distillation, wherein the temperature of the vacuum distillation is 40 to 90° C. and the vacuum degree is 10 to 10000 Pa.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The fluorine-containing solvent is hexafluoropropylene trimer, and the mass ratio of the hexafluoropropylene trimer to polytetrafluoroethylene micropowder and perfluoropolyether oil is 6-10:4:6-12.

10. The perfluoropolyether grease prepared by the preparation method according to any one of claims 1 to 9.

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