Grease for vacuum actuators

Abstract

The present invention relates to a grease for vacuum actuators, comprising the following components (a) and (b): (a) a perfluoropolyether as a base oil, having a kinematic viscosity of 100 mm² / s or more but less than 200 mm² / s at 40°C and a vapor pressure of 1.0 × 10⁻⁷ Pa or less at 20°C; and (b) polytetrafluoroethylene as a thickener, wherein the grease has a shear viscosity of 4500 mPa·s or less at 25°C.

Description

Technical Field

[0001] This invention relates to a lubricating grease for vacuum actuators. Prior Technology

[0002] In the manufacture of flat panel displays such as liquid crystal displays and organic EL displays, or in the manufacture of semiconductor devices, vacuum chambers are used to move substrates or the like towards the processing section of the device within a vacuum to perform various processes. In this case, a vacuum actuator such as a rotary guide is used to introduce driving force from a drive source located outside the vacuum into the vacuum chamber.

[0003] This type of vacuum actuator requires maintaining the airtightness necessary to sustain the vacuum and transmitting the driving force from the outside to the inside of the vacuum chamber. Therefore, for a vacuum actuator, it is essential to have a tight seal on the sliding surface under vacuum conditions.

[0004] As a means of ensuring the sealing of sliding surfaces under vacuum, sealing devices with annular sealing portions formed of elastic materials are known. For example, Patent Document 1 describes a sealing device that can stably maintain sealing and suppress the consumption of lubricant.

[0005] In addition, grease is sometimes used in vacuum actuators to achieve lubrication on the sliding surfaces. The use of grease can, for example, prevent wear on the sliding surfaces and prevent deterioration of the seal under vacuum conditions. However, even when grease is used in vacuum actuators, it is not easy to maintain good lubrication over a long period, and a grease that can achieve this is required. [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-090479 Summary of the Invention

[0007] [The problem that the invention aims to solve] The present invention provides a grease for vacuum actuators that can maintain good lubrication in vacuum actuators for a long time. [Methods for solving problems]

[0008] An embodiment of the present invention is a grease for a vacuum actuator, comprising the following components (a) and (b): (a) The perfluoropolyether used as a base oil has a kinematic viscosity of 100 mm² / s or more but less than 200 mm² / s at 40°C and a vapor pressure of 1.0 × 10⁻⁷ Pa or less at 20°C; (b) Polytetrafluoroethylene as a thickener The grease has a shear viscosity of less than 4500 mPa·s at 25°C. [Effects of the Invention]

[0009] According to the present invention, a grease for vacuum actuators can be provided that can maintain a good lubrication state in a vacuum actuator for a long period of time. Implementation

[0010] [Forms of Invention Implementation] The vacuum actuator grease of this embodiment comprises: (a) a perfluoropolyether as a base oil, having a kinematic viscosity of 100 mm² / s or more but less than 200 mm² / s at 40°C and a vapor pressure of 1.0 × 10⁻⁷ Pa or less at 20°C; and (b) polytetrafluoroethylene as a thickener, wherein the grease has a shear viscosity of 4500 mPa·s or less at 25°C. The components contained in the vacuum actuator grease, as well as its composition and properties, will be described in detail below.

[0011] <Base oil> The grease for vacuum actuators contains perfluoropolyether as a base oil. The kinematic viscosity of the perfluoropolyether at 40°C is 100 mm² / s or more but less than 200 mm² / s, with an upper limit preferably below 190 mm² / s, more preferably below 180 mm² / s, and even more preferably below 170 mm² / s. Furthermore, the lower limit of the kinematic viscosity of the perfluoropolyether at 40°C is preferably above 110 mm² / s, more preferably above 120 mm² / s, and even more preferably above 130 mm² / s. By controlling the kinematic viscosity of the perfluoropolyether at 40°C, the shear viscosity of the grease at 25°C can be easily controlled within a suitable range, and good lubrication can be easily maintained over a long period in vacuum actuators using the grease. The kinematic viscosity of the perfluoropolyether at 40°C is measured according to JIS K 2220:2023. This type of base oil can be used alone or in combination with two or more types.

[0012] Furthermore, the vapor pressure of perfluoropolyether at 20°C is below 1.0 × 10⁻⁷ Pa, with no particular limitation on the lower limit, but preferably above 1.0 × 10⁻¹³ Pa, more preferably above 1.0 × 10⁻¹² Pa, even more preferably above 1.0 × 10⁻¹¹ Pa, and particularly preferably above 1.0 × 10⁻¹⁰ Pa. The upper limit of the vapor pressure of perfluoropolyether at 20°C is preferably below 1.0 × 10⁻⁸ Pa, more preferably below 1.0 × 10⁻⁹ Pa. By controlling the vapor pressure of perfluoropolyether at 20°C, the evaporation rate of perfluoropolyether under reduced pressure can be easily suppressed, preventing contamination within the vacuum chamber. The vapor pressure of perfluoropolyether at 20°C is determined using the Knudsen diffusion method.

[0013] The grease for vacuum actuators preferably contains 70% to 99% perfluoropolyether by weight relative to the total mass of the grease, more preferably 75% to 95% perfluoropolyether, and even more preferably 80% to 90% perfluoropolyether.

[0014] Thickener The grease for vacuum actuators contains polytetrafluoroethylene (PTFE) as a thickener, and preferably contains PTFE particles. The primary particle size of the PTFE particles is not particularly limited, but is preferably 0.01 μm to 0.50 μm, more preferably 0.03 μm to 0.30 μm, and even more preferably 0.05 μm to 0.15 μm. By controlling the primary particle size of the PTFE particles, the shear viscosity of the grease at 25°C can be easily controlled within a suitable range, and good lubrication can be easily maintained over a long period in vacuum actuators using the grease. The primary particle size of the PTFE particles is determined by image analysis of photographs taken with a scanning electron microscope (SEM). This thickener can be used alone or in combination with two or more other thickeners.

[0015] The grease for vacuum actuators preferably contains 1% to 30% by mass of polytetrafluoroethylene (PTFE) relative to the total mass of the grease, more preferably 5% to 25% by mass, and even more preferably 10% to 20% by mass of PTFE.

[0016] Composition and properties of grease for vacuum actuators The shear viscosity of the grease for vacuum actuators at 25°C is 4500 mPa·s or less. The lower limit of the shear viscosity at 25°C is not particularly limited, but preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, and even more preferably 1500 mPa·s or more. Furthermore, the upper limit of the shear viscosity of the grease for vacuum actuators at 25°C is preferably 3700 mPa·s or less, more preferably 3500 mPa·s or less, even more preferably 3000 mPa·s or less, and particularly preferably 2500 mPa·s or less. The shear viscosity of the grease for vacuum actuators at 25°C can be controlled by, for example, the content of components (a) and (b), the kinematic viscosity of perfluoropolyether (component (a)) at 40°C, and the primary particle size of polytetrafluoroethylene (component (b)). By controlling the shear viscosity of the grease used in vacuum actuators at 25°C, for example, the resistance of the sliding surface of the vacuum actuator is reduced, making stick-slip less likely and suppressing wear. Therefore, it is easy to maintain a good lubrication state for a long time in vacuum actuators using grease. The shear viscosity of the grease used in vacuum actuators at 25°C is as described in the examples described later, for example, using a cone-plate rotational viscometer, at 25°C, the shear viscosity value is obtained when the shear rate is 300 s⁻¹ after the shear rate increases from 0 s⁻¹ to 360 s⁻¹ in 180 seconds.

[0017] Furthermore, according to JIS K 2220:2023, the kneading penetration of the grease for vacuum actuators is preferably 100 to 500, more preferably 200 to 400, even more preferably 250 to 350, and especially preferably 280 to 330.

[0018] Furthermore, the evaporation loss of the grease for vacuum actuators, as measured in accordance with JIS K 2220:2023 (test temperature 99°C, 22 hours), is preferably 0.01% by mass or more and 0.5% by mass or more, and more preferably 0.05% by mass or more and 0.2% by mass or less.

[0019] The grease used for vacuum actuators is preferably made entirely of materials other than perfluoropolyether and polytetrafluoroethylene (PTFE). This means that the grease for vacuum actuators is composed only of perfluoropolyether and PTFE, or only of perfluoropolyether, PTFE, and unavoidable impurities (impurities that are unavoidably mixed in during the manufacturing of the grease). This makes it easier to prevent contamination within the vacuum chamber.

[0020] The grease for vacuum actuators is preferably composed of components (a) and (b). In this case, it means that the grease for vacuum actuators is composed of only components (a) and (b), or only components (a), components (b) and unavoidable impurities.

[0021] The mass ratio of component (a) to component (b) in the grease used for vacuum actuators is preferably 3:1 to 5:1, and more preferably 4:1 to 5:1.

[0022] The vacuum actuator grease of this embodiment can be used in vacuum actuators having, for example, the following components: a partition wall separating the vacuum side space from the atmospheric side space; a shaft member that transmits driving force through the partition wall; and a sealing member that slides relative to a sliding surface disposed on the partition wall and formed on the outer periphery of the shaft member, sealing the vacuum side space from the atmospheric side space. Furthermore, the vacuum actuator grease of this embodiment has various applications, such as in lubricant compositions for vacuum actuators equipped with vacuum seals using lip seals.

[0023] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments and includes various forms included in the concept of the present invention and the scope of the patent application. Various changes can be made within the scope of the present invention.

[0024] Based on the above embodiments, the present invention relates to the following [1]~[6]: [1] A grease for a vacuum actuator, characterized in that it comprises the following components (a) and (b): (a) The perfluoropolyether used as a base oil has a kinematic viscosity of 100 mm² / s or more but less than 200 mm² / s at 40°C and a vapor pressure of 1.0 × 10⁻⁷ Pa or less at 20°C; (b) Polytetrafluoroethylene as a thickener The grease has a shear viscosity of less than 4500 mPa·s at 25°C. [2] The vacuum actuator grease as described in [1] above, wherein the aforementioned perfluoropolyether has a dynamic viscosity of less than 180 mm2 / s at 40°C. [3] The vacuum actuator grease as described in [1] or [2] above, wherein, relative to the total mass of the aforementioned vacuum actuator grease, it contains 80% by mass and 99% by mass of the aforementioned perfluoropolyether and 1% by mass and 20% by mass of the aforementioned polytetrafluoroethylene. [4] The vacuum actuator grease of any of [1] to [3] above contains particles of the aforementioned polytetrafluoroethylene with a primary particle size of 0.05 μm to 0.15 μm. [5] The vacuum actuator grease of any of [1] to [4] above has a shear viscosity of 3700 mPa·s or less at the aforementioned 25°C. [6] The vacuum actuator grease as described in any of [1] to [5] above is composed of the aforementioned components (a) and (b). [Example]

[0025] The present invention will be described in more detail below with reference to embodiments and the like, but the present invention is not limited by these embodiments and the like.

[0026] <Preparation of Lubricating Grease> (Examples 1-4, Comparative Examples 1-4) The base oil (perfluoropolyether, PFPE) and thickener (polytetrafluoroethylene, PTFE) listed in Table 1 are mixed in the proportions specified in Table 1 below to obtain a homogeneous grease.

[0027] <Kinetic viscosity> The kinematic viscosity (mm² / s) of PFPE at 40°C was determined according to JIS K 2220:2023. The vapor pressure (Pa) of PFPE at 20°C was determined by the Knudsen exudation method. The primary particle size (μm) of PTFE was determined by image analysis of polytetrafluoroethylene particles obtained using SEM. The results are shown in Table 1.

[0028] <Shear viscosity> The shear viscosity (mPa·s) of the lubricating grease at 25°C was determined using a cone-plate rotational viscometer (Anton Paar), with a cone plate of 25 mm diameter and a cone angle of 1°. Measurements were taken at 25°C, with the shear rate increased from 0 s⁻¹ to 360 s⁻¹ over 180 seconds. The shear viscosity at a shear rate of 300 s⁻¹ was taken as the shear viscosity of the lubricating grease at 25°C. The results are shown in Table 1.

[0029] <Pinching and Needle Penetration, Evaporation Loss> The pinch and penetration of the grease were determined according to JIS K 2220:2023; the evaporation loss (mass%) of the grease was determined according to JIS K 2220:2023 (test temperature 99℃, 22 hours). The results are shown in Table 1.

[0030] (Evaluation of grease) The obtained grease was subjected to the following durability test.

[0031] <Durability Testing> The obtained grease is used in the sealing sliding part of the vacuum actuator equipped in the vacuum chamber. Using this vacuum actuator, under the following test conditions, the actuator is rotated 180 degrees from the origin in a forward motion, then rotated 180 degrees in a reverse motion and returned to the origin. This cycle is repeated up to a maximum of 3 million times. In this test, the number of cycles (endurance cycles) until the following vacuum conditions cannot be maintained is measured. The results are shown in Table 1. Furthermore, the test is terminated at the point when the following vacuum conditions cannot be maintained.

[0032] (Experimental conditions) Rotation number: The rotation number is taken when the maximum circumferential speed of the sealed sliding part of the vacuum actuator is 0.3 m / sec. Load conditions: Moment load is set to no load, and torsion load is set to the load generated only by the sliding resistance of the seal. Vacuum conditions: The vacuum level in the vacuum chamber is defined as below 1.0 × 10⁻⁵ Pa. If the sealing and sliding parts of the vacuum actuator cannot be adequately lubricated, stick-slip will occur, leading to vacuum leakage, and thus the aforementioned vacuum conditions cannot be maintained. In this case, it is determined that the vacuum actuator can no longer be used, and the endurance test is terminated even if 3 million cycles have not been reached.

[0033]

[0034] The blending materials for each component in Table 1 above are as follows: PFPE A:FM30 (Made by Solvay SA, "FOMBLIN (registered trademark) M30") PFPE B:DS200 (Daikin Industries, Ltd. "DEMNUM (registered trademark) S-200") PFPE C:FM60 (Made by Solvay SA, "FOMBLIN (registered trademark) M60") PFPE D:B400V (NOK KLUBER company manufactures "BARRIERTA J 400 V")

[0035] As shown in Table 1, by using PFPE as a base oil with a kinematic viscosity of 100 mm² / s or more but less than 200 mm² / s at 40°C and a vapor pressure of 1.0 × 10⁻⁷ Pa or less at 20°C, and PTFE as a thickener, and having a shear viscosity of 4500 mPa·s or less (25°C), a vacuum actuator grease that can maintain good lubrication for a long time can be obtained (Examples 1-4). In particular, the greases of Examples 1-3, which have a shear viscosity of 3700 mPa·s or less at 25°C, have completed 3 million cycles in the durability test, demonstrating even better durability.

[0036] On the other hand, the greases of Comparative Examples 1 to 4, which use perfluoropolyether with a dynamic viscosity of 200 mm² / s or more at 40°C, all have a shear viscosity of over 4500 mPa·s at 25°C and a durability test cycle of 300,000 cycles, indicating poor durability.

Claims

1. A grease for a vacuum actuator, characterized in that it comprises the following components (a) and (b): (a) a perfluoropolyether as a base oil, having a kinematic viscosity of 100 mm² / s or more but less than 200 mm² / s at 40°C and a vapor pressure of 1.0 × 10⁻⁷ Pa or less at 20°C; (b) polytetrafluoroethylene as a thickener, wherein the grease has a shear viscosity of 4500 mPa·s or less at 25°C.

2. The grease for vacuum actuators as claimed in claim 1, wherein the aforementioned perfluoropolyether has a kinematic viscosity of less than 180 mm² / s at 40°C.

3. The vacuum actuator grease as claimed in claim 1, wherein, relative to the total mass of the aforementioned vacuum actuator grease, it contains 80% to 99% by mass of the aforementioned perfluoropolyether and 1% to 20% by mass of the aforementioned polytetrafluoroethylene.

4. The vacuum actuator grease as claimed in claim 1, which contains particles of the aforementioned polytetrafluoroethylene with a primary particle size of 0.05 μm to 0.15 μm.

5. The grease for vacuum actuators as claimed in claim 1 has a shear viscosity of 3700 mPa·s or less at the aforementioned 25°C.

6. The vacuum actuator grease of any one of claims 1 to 5 is composed of the aforementioned components (a) and (b).