Grease for vacuum actuator

Abstract

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

Description

Grease for vacuum actuators

[0001] This invention relates to grease for vacuum actuators.

[0002] In the manufacturing of flat panel displays such as liquid crystal displays and organic EL displays, or in the manufacturing of semiconductor devices, a vacuum chamber is used to move substrates and other materials to the processing unit of the device for various processes within a vacuum. In this process, a vacuum actuator, such as a rotary drive unit, is used to introduce driving force from a drive source located outside the vacuum into the vacuum chamber.

[0003] Such vacuum actuators are required to maintain sealing properties to preserve the vacuum, as well as to transmit driving force from the outside to the inside of the vacuum chamber. Therefore, it is essential that vacuum actuators have sealing properties at their sliding surfaces in a vacuum state.

[0004] As a means of ensuring sealing performance at sliding surfaces in a vacuum, a sealing device equipped with an annular sealing portion made of an elastic material is known. For example, Patent Document 1 describes a sealing device that can stably maintain sealing performance and reduce the amount of lubricant consumed.

[0005] Incidentally, grease is sometimes used in vacuum actuators to provide lubrication to the sliding surfaces. By using grease, for example, wear progression on the sliding surfaces can be prevented, and the deterioration of sealing performance in a vacuum state can be prevented. However, even when grease is used in vacuum actuators, it is difficult to maintain a good lubrication state over a long period of time, and there is a need for a grease that can do this.

[0006] Japanese Patent Publication No. 2019-090479

[0007] The present invention provides a grease for vacuum actuators that enables the maintenance of a good lubrication state in a vacuum actuator over a long period of time.

[0008] Embodiments of the present invention include the following components (a) and (b): (a) Base oil having a kinematic viscosity of 100 mm at 40°C ２100 mm2 / s or more and less than 200 mm2 / s ２ less than 100 mm2 / s, and the vapor pressure at 20°C is 1.0 × 10 －７ Pa or less. The grease for a vacuum actuator contains (b) a thickener containing polytetrafluoroethylene and has a shear viscosity at 25°C of 4500 mPa·s or less.

[0009]

[0009] According to the present invention, it is possible to provide a grease for a vacuum actuator that enables a good lubrication state to be maintained in the vacuum actuator for a long time.

[0010]

[0010] The grease for a vacuum actuator according to the present embodiment contains, as a base oil, a perfluoropolyether having a kinematic viscosity at 40°C of 100 mm2 / s ２ ２ 100 mm2 / s or more and less than 200 mm2 / s ２ less than 100 mm2 / s, and the vapor pressure at 20°C is 1.0 × 10 －７ Pa or less. As a thickener, it contains polytetrafluoroethylene and has a shear viscosity at 25°C of 4500 mPa·s or less. Hereinafter, the components contained in the grease for a vacuum actuator, the composition and properties of the grease for a vacuum actuator, etc. will be described in detail.

[0011]

[0011] <Base oil> The grease for a vacuum actuator contains a perfluoropolyether as a base oil. The kinematic viscosity at 40°C of the perfluoropolyether is 100 mm2 / s ２ ２ 100 mm2 / s or more and less than 200 mm2 / s ２ less than 200 mm2 / s, and its upper limit is preferably 190 mm2 / s ２ ２ or less, more preferably 180 mm2 / s ２ ２ or less, and even more preferably 170 mm2 / s ２ ２ or less. Further, the lower limit of the kinematic viscosity at 40°C of the perfluoropolyether is preferably 110 mm2 / s<0^{2} / s ２ ２ or more, more preferably 120 mm2 / s ２ ２ or more, and even more preferably 130 mm2 / s ２ ２It is even more preferable that the kinematic viscosity is 1 / s or higher. By controlling the kinematic viscosity of the perfluoropolyether at 40°C, it becomes easier to control the shear viscosity of the grease at 25°C to a suitable range, and it becomes easier to maintain a good lubrication state over a long period of time in the vacuum actuator in which the grease is used. The kinematic viscosity of the perfluoropolyether at 40°C is measured according to JIS K 2220:2023. Such base oils may be used alone or as a mixture of two or more types.

[0012] Furthermore, the vapor pressure of perfluoropolyether at 20°C is 1.0 × 10⁻⁶. －７ It is less than or equal to Pa, and there is no particular lower limit, but 1.0 × 10 －１３ It is preferable that the pressure be Pa or higher, and 1.0 × 10 －１２ It is more preferable that the pressure be Pa or higher, and 1.0 × 10 －１１ It is even more preferable that the pressure be Pa or higher, and 1.0 × 10 －１０ It is particularly preferable that the vapor pressure be Pa or higher. Furthermore, the upper limit of the vapor pressure of perfluoropolyether at 20°C is 1.0 × 10⁻⁶. －８ It is preferable that it be Pa or less, and 1.0 × 10 －９ It is more preferable that the vapor pressure be Pa or less. By controlling the vapor pressure of perfluoropolyether at 20°C, the amount of evaporation of perfluoropolyether under reduced pressure can be suppressed, making it easier to prevent contamination in the vacuum chamber. The vapor pressure of perfluoropolyether at 20°C is measured by the Knudsen fusion method.

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

[0014] <Thickener> The grease for vacuum actuators contains polytetrafluoroethylene as a thickener, preferably polytetrafluoroethylene particles. The primary particle size of the polytetrafluoroethylene particles is not particularly limited, but is preferably 0.01 μm or more and 0.50 μm or less, more preferably 0.03 μm or more and 0.30 μm or less, and even more preferably 0.05 μm or more and 0.15 μm or less. By controlling the primary particle size of the polytetrafluoroethylene particles, it becomes easier to control the shear viscosity of the grease at 25°C to a suitable range, and it becomes easier to maintain a good lubrication state over a long period of time in the vacuum actuator in which the grease is used. The primary particle size of the polytetrafluoroethylene particles is measured by taking a photograph of the polytetrafluoroethylene particles with a scanning electron microscope (SEM) and then performing image analysis on the photograph. Such thickeners may be used alone or in mixtures of two or more types.

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

[0016] <Composition and Characteristics of Vacuum Actuator Grease> The shear viscosity of the vacuum actuator grease at 25°C is 4500 mPa·s or less. The lower limit of the shear viscosity at 25°C is not particularly limited, but it is preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, and even more preferably 1500 mPa·s or more. The upper limit of the shear viscosity of the vacuum actuator grease 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 vacuum actuator grease at 25°C can be controlled, for example, by the content of components (a) and (b), the kinematic viscosity of perfluoropolyether (component (a)) at 40°C, and the primary particle size of the polytetrafluoroethylene (component (b)) particles. By controlling the shear viscosity of vacuum actuator grease at 25°C, for example, the resistance of the sliding surfaces in the vacuum actuator can be reduced, stick-slip is less likely to occur, and wear is suppressed, making it easier to maintain a good lubrication state over a long period of time in vacuum actuators using grease. The shear viscosity of vacuum actuator grease at 25°C is determined, for example, using a cone-plate type rotational viscometer at 25°C, by measuring 0 s over 180 seconds, as described in the examples below. －１ From 360s －１ This is measured when the shear rate is increased to 300 s. －１ This is the value of the shear viscosity at that time.

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

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

[0019] It is preferable that the grease for vacuum actuators is substantially free of materials other than perfluoropolyether and polytetrafluoroethylene. This means that the grease for vacuum actuators consists only of perfluoropolyether and polytetrafluoroethylene, or only of perfluoropolyether, polytetrafluoroethylene, and unavoidable impurities (impurities that inevitably get mixed in during the manufacture of grease). This makes it easier to prevent contamination inside the vacuum chamber.

[0020] The grease for the vacuum actuator preferably consists of components (a) and (b). In this case, the grease for the vacuum actuator may consist only of components (a) and (b), or only of components (a), (b), and unavoidable impurities.

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

[0022] The vacuum actuator grease according to this embodiment can be used in a vacuum actuator having, for example, a partition wall separating a vacuum-side space from an atmospheric-side space, a shaft member that penetrates the partition wall and transmits driving force, and a sealing member that is provided on the partition wall and slides against a sliding surface formed on the outer circumference of the shaft member, thereby sealing the vacuum-side space from the atmospheric-side space. Furthermore, the vacuum actuator grease according to this embodiment is useful for various applications, such as a lubricant composition for a vacuum actuator equipped with a vacuum seal using a lip.

[0023] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concept and claims of the present invention, and can be modified in various ways within the scope of the present invention.

[0024] Based on the embodiments described above, the present invention relates to the following [1] to [6]. [1] The following components (a) and (b): (a) As a base oil, having a kinematic viscosity of 100 mm at 40°C ２ / s or more 200mm ２ It is less than / s, and the vapor pressure at 20°C is 1.0 × 10⁻⁶. －７ (b) A vacuum actuator grease characterized by comprising a perfluoropolyether having a shear viscosity of Pa or less, (b) polytetrafluoroethylene as a thickener, and having a shear viscosity of 4500 mPa·s or less at 25°C. [2] The kinematic viscosity of the perfluoropolyether at 40°C is 180 mm ２ [1] above, the vacuum actuator grease having a viscosity of 0.5 mPa·s or less. [3] The vacuum actuator grease according to [1] or [2] above, comprising 80% to 99% by mass of the perfluoropolyether and 1% to 20% by mass of the polytetrafluoroethylene, based on the total mass of the vacuum actuator grease. [4] The vacuum actuator grease according to any one of [1] to [3] above, comprising polytetrafluoroethylene particles having a primary particle diameter of 0.05 μm to 0.15 μm. [5] The vacuum actuator grease according to any one of [1] to [4] above, having a shear viscosity of 3700 mPa·s or less at 25°C. [6] The vacuum actuator grease according to any one of [1] to [5] above, comprising components (a) and (b).

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

[0026] <Preparation of Grease> (Examples 1 to 4, Comparative Examples 1 to 4)The base oils (perfluoropolyether, PFPE) and thickeners (polytetrafluoroethylene, PTFE) described in Table 1 below were mixed at the compounding ratios described in Table 1 to obtain a uniform grease.

[0027] <Kinematic Viscosity>The kinematic viscosity (mm ２ / s) of PFPE at 40 °C was measured according to JIS K 2220:2023. The vapor pressure (Pa) of PFPE at 20 °C was measured by the Knudsen effusion method. The primary particle size (μm) of PTFE was measured by taking a photograph of the polytetrafluoroethylene particles with a SEM and then analyzing the photograph by image analysis. The results are shown in Table 1.

[0028] <Shear Viscosity>To measure the shear viscosity (mPa·s) of the grease at 25 °C, a cone-plate type rotational viscometer (manufactured by Anton Paar) was used. At that time, a cone-plate with a diameter of 25 mm and a cone angle of 1° was used. The measurement was carried out at 25 °C, and the shear rate was increased from 0 s －１ to 360 s －１ The shear viscosity when the shear rate reached 300 s －１ was taken as the shear viscosity of the grease at 25 °C. The results are shown in Table 1.

[0029] <Degree of Miscibility, Evaporation Loss>The degree of miscibility of the grease was measured according to JIS K 2220:2023, and the evaporation loss (mass %) of the grease was measured according to JIS K 2220:2023 (test temperature 99 °C, 22 hours). The results are shown in Table 1.

[0030] <Evaluation of Grease> The following durability test was conducted on the obtained grease.

[0031] <Durability Test> The obtained grease was used on the seal sliding part of a vacuum actuator installed in a vacuum chamber. Using this vacuum actuator, a test was conducted under the following test conditions, in which a cycle of rotating 180 degrees from the origin in the forward direction and then rotating 180 degrees in the reverse direction to return to the origin was repeated up to a maximum of 3 million times. In this test, the number of cycles until the vacuum conditions described below could no longer be maintained (durability cycles) was measured. The results are shown in Table 1. Note that the test was terminated at the point when the vacuum conditions described below could no longer be maintained.

[0032] (Test conditions) Rotation speed: The rotation speed shall be such that the maximum peripheral speed at the seal sliding part provided on the vacuum actuator is 0.3 m / sec. Load conditions: There shall be no moment load, and the torque load shall be only the load due to the sliding resistance of the seal. Vacuum conditions: The vacuum level inside the vacuum chamber shall be 1.0 × 10⁻⁶. －５ The condition is that the pressure must be below Pa. If the good lubrication state of the seal sliding part of the vacuum actuator cannot be sufficiently maintained, stick-slip or the like will occur in the seal sliding part, leading to vacuum leakage, and thus the above vacuum conditions cannot be maintained. In this case, it was determined that it would be difficult to continue using the vacuum actuator, and the durability test was terminated even if 3 million cycles were not reached.

[0033]

[0034] The compositional materials for each component in Table 1 above are as follows: PFPE A: FM30 (Solvay S.A.'s "FOMBLIN® M30") PFPE B: DS200 (Daikin Industries' "DEMNUM® S-200") PFPE C: FM60 (Solvay S.A.'s "FOMBLIN® M60") PFPE D: B400V (NOK Klüber's "BARRIERTA J 400 V")

[0035] As shown in Table 1, the grease, as a base oil, has a kinematic viscosity of 100 mm at 40°C. ２ / s or more 200mm ２ It is less than / s, and the vapor pressure at 20°C is 1.0 × 10⁻⁶. －７We were able to obtain a vacuum actuator grease that can maintain a good lubrication state over a long period of time by containing PFPE with a shear viscosity of Pa or less, PTFE as a thickener, and having a shear viscosity of 4500 mPa·s or less (at 25°C) (Examples 1 to 4). In particular, the greases of Examples 1 to 3, which had a shear viscosity of 3700 mPa·s or less at 25°C, completed 3 million cycles in durability tests, demonstrating superior durability.

[0036] On the other hand, the kinematic viscosity at 40°C is 200 mm². ２ The greases in Comparative Examples 1 to 4, which used perfluoropolyether with a viscosity of 1 / s or higher, all had a shear viscosity at 25°C exceeding 4500 mPa·s, and in durability tests, they had a durability of 300,000 cycles, indicating poor durability.

Claims

1. The following components (a) and (b): (a) Base oil with a kinematic viscosity of 100 mm at 40°C ２ / s or more 200mm ２ It is less than / s, and the vapor pressure at 20°C is 1.0 × 10⁻⁶. －７ A vacuum actuator grease characterized by comprising (b) a perfluoropolyether with a shear viscosity of Pa or less, (b) polytetrafluoroethylene as a thickener, and having a shear viscosity of 4500 mPa·s or less at 25°C.

2. The kinematic viscosity of the perfluoropolyether at 40°C is 180 mm². ２ The vacuum actuator grease according to claim 1, wherein the value is less than or equal to / s.

3. The vacuum actuator grease according to claim 1, comprising 80% by mass or more and 99% by mass or less of the perfluoropolyether and 1% by mass or more and 20% by mass or less of the polytetrafluoroethylene, based on the total mass of the vacuum actuator grease.

4. The vacuum actuator grease according to claim 1, comprising polytetrafluoroethylene particles having a primary particle diameter of 0.05 μm or more and 0.15 μm or less.

5. The vacuum actuator grease according to claim 1, wherein the shear viscosity at 25°C is 3700 mPa·s or less.

6. A vacuum actuator grease according to any one of claims 1 to 5, comprising components (a) and (b).

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