JP2005281511A - Grease composition and direct acting equipment filled with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grease composition which has a long service life, even when a low viscosity base oil is used and serves to materialize low torque direct acting equipment and direct acting equipment filled with the composition. <P>SOLUTION: The grease composition contains a base oil having a dynamic viscosity of 14-70 mm<SP>2</SP>/s at 40°C, a thickener containing at least one kind selected from lithium stearate, lithium 12-hydroxy stearate and a specific diurea compound, an extreme pressure additive containing at least one kind selected from molybdenum dithiophosphate, molybdenum dithiocarbamate and thiophosphates. The mixing ratio of the thickener is 10-17 wt.% of the total amount of the grease composition. The mixing ratio of the extreme pressure additive is 1-5 wt.% of the total amount of the grease composition. The grease composition has a working penetration of 230-320. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement of a grease composition and a linear motion device in which the improved grease composition is enclosed, and more particularly to high performance and durability in a reciprocating motion in which such an improved grease composition is enclosed. It relates to an excellent linear motion device.

  In recent years, power saving and high-speed rotation of linear motion devices have been promoted, and thus low torque performance has been regarded as important. This is because in a high-torque device, as the rotational speed increases, friction / torque increases to generate heat and motor overload, hindering power saving and high-speed rotation.

By the way, the lubricant for the conventional linear motion device includes a base soap, a lithium soap / mineral grease using lithium soap as a mineral oil and a thickener, a base oil, an ester synthetic oil and a lithium as a thickener. Lithium soap / ester oil based grease using soap is mainly used. And it is the present condition that there are many things of 220-280 as a conventional base oil kinematic viscosity, and 25-200 mm < ² > / s (40 degreeC), and a consistency (for example, refer patent document 1).

Further, the torque of the linear motion device is generated due to friction caused by minute sliding on the rolling contact surface, sliding friction on the sliding contact surface, viscous resistance of grease, and the like. Among these, the viscosity resistance of grease is affected by the kinematic viscosity of grease base oil, the consistency of grease, and the blending amount of thickener. Therefore, use a base oil with a low kinematic viscosity or increase the consistency. In addition, reducing the blending amount of the thickener is effective in reducing the viscous resistance of the grease.
JP 2003-294107 A

  However, when the base oil kinematic viscosity of the grease is reduced, the oil film thickness on the lubrication surface becomes thin, which causes problems in lubrication performance and may cause damage such as wear and seizure. In addition, base oils with low kinematic viscosity usually have low heat resistance, which may cause problems with durability performance in a high temperature atmosphere.

  On the other hand, when the grease consistency is increased, the content of the thickener in the grease is relatively reduced, the resistance to mechanical shearing is weakened, and the softening leakage and impact resistance of the grease during linear motion operation are problematic. It becomes. Also, reducing the amount of grease enclosed in the movable body of the linear motion device is effective in reducing torque, but may cause poor lubrication. Furthermore, as a phenomenon peculiar to the ball screw, a load due to acceleration / deceleration is repeatedly applied at the time of starting and stopping. In such a case, if the amount of the thickener is large or the viscosity is high, there is a damper effect, but there is no effect in reducing the torque.

  Accordingly, in view of the above circumstances, an object of the present invention is to provide a grease composition for realizing a linear motion device that has a long life and uses a low viscosity base oil, and encloses the grease composition. To provide a linear motion device.

As a result of intensive studies to solve the above-mentioned problems, the present inventor formulated a specific amount of a specific thickener and an extreme pressure additive in a grease composition, and mixed the grease composition in a specific range. Thus, the present invention has been completed. That is, the object is selected from a base oil having a base oil kinematic viscosity of 14 to 70 mm ² / s at 40 ° C., lithium stearate, lithium 12-hydroxystearate, and diurea compounds represented by the following formulas I and II. A grease composition comprising a thickener containing at least one selected from the group, and an extreme pressure additive containing at least one selected from molybdenum dithiophosphate, molybdenum dithiocarbamate, and thiophosphate. The amount is 8 to 17% by weight with respect to the total amount of the grease composition, and the amount of the extreme pressure additive is 1 to 5% by weight with respect to the total amount of the grease composition. This is achieved by a grease composition having a product penetration of 230-320.

（ここで、Ｒ¹およびＲ²は各々独立に、炭素数８〜１８の直鎖状のアルキル基を表す。）
本発明の好ましい態様によれば、前記グリース組成物において、前記基油がポリオールエステル油またはポリα−オレフィン油から選ばれる少なくとも一種を含む、かつ、前記ポリオールエステル油またはポリα−オレフィン油が、前記基油の全量に対して８０重量％以上含有することを特徴とする。
また、上記目的は、前記グリース組成物を封入した、直動装置により達成される。

(Here, R ¹ and R ² each independently represents a linear alkyl group having 8 to 18 carbon atoms.)
According to a preferred aspect of the present invention, in the grease composition, the base oil contains at least one selected from a polyol ester oil or a poly α-olefin oil, and the polyol ester oil or the poly α-olefin oil comprises: 80% by weight or more based on the total amount of the base oil.
The above object is achieved by a linear motion device in which the grease composition is enclosed.

  According to the grease composition of the present invention, a grease composition having a long life even when a low-viscosity base oil is used is realized, and the linear motion device in which such a grease composition is enclosed provides a low torque linear motion device. To do.

  Hereinafter, the present invention will be described in detail. In addition, embodiment mentioned later is an illustration for demonstrating this invention, and is not the meaning which limits this invention only to this embodiment. The present invention can be implemented in various forms without departing from the gist thereof.

  First, a linear motion device to which the grease composition according to the present invention is applied will be described, but the configuration and structure of the specific linear motion device itself are not limited. FIG. 1 is a cross-sectional view showing a ball screw device used as an embodiment of a linear motion device according to the present invention incorporated in a semiconductor or liquid crystal manufacturing apparatus. In this ball screw device, a ball screw shaft 10 having a spiral ball screw groove 12 formed on the outer peripheral surface thereof, and a spiral ball screw groove 24 facing the ball screw groove 12 of the screw shaft 10 has an inner peripheral surface 22. The ball nut 20 formed in the above-mentioned shape, the ball screw groove 12 of the screw shaft 10 and the ball screw groove 24 of the ball nut 20 face each other in a spiral ball rolling space so as to be freely rollable. And a tube-type circulation path 40 that circulates these balls 30. The tube-type circulation path 40 is composed of a tube having an approximately U-shaped outer shape, and both end portions 42 of the tube-type circulation path 40 are respectively inserted into the ball rolling space in the ball nut 20 through tube mounting holes 29 penetrating the ball nut 20 in the radial direction. The stopper 46 is fixed to the outer surface of the ball nut 20. The ball 30 that rolls in the spiral ball rolling space moves around the ball screw grooves 12 and 24 a plurality of times and is then scooped up at one end 42 of the tube-type circulation path 40, so that the tube-type circulation The circulation through the path 40 and returning from the other end 42 to the ball rolling space in the ball nut 20 is repeated.

  Circular recesses 26 are formed in the openings at both ends of the ball nut 20, and the inner peripheral surface of the disc-shaped seal member 28 fitted to this is the outer peripheral surface of the ball screw shaft 10 and the ball screw groove 12. The ball screw device is sealed in sliding contact with the surface. According to such a linear motion device, since the ball screw shaft 10 and the ball nut 20 are in contact with each other through the rolling of the ball 30, the ball nut 20 is relatively helical with respect to the ball screw shaft 10 with a small driving force. Can exercise.

Next, the grease composition according to the present invention enclosed in the linear motion device shown above will be described. The base oil of the present invention uses a low viscosity base oil having a kinematic viscosity at 40 ° C. of 14 to 70 mm ² / s. Specific examples of base oils include polyol ester oil (hereinafter referred to as “POE”) or poly α-olefin oil (hereinafter referred to as “PAO”) in consideration of fluidity at low temperature and durability at high temperature. What has at least 1 type chosen as a main component is preferable.

  Examples of POE include oils obtained by appropriately reacting the following polyhydric alcohols and monobasic acids. The monobasic acid to be reacted with the polyhydric alcohol may be used alone or in combination. Furthermore, you may use as complex ester which is ester of polyhydric alcohol and the mixed fatty acid of a dibasic acid and a monobasic acid. Examples of the polyhydric alcohol include, but are not limited to, trimethylolpropane, pentaerythritol, dipentaerythritol, neopentyl glycol, 2-methyl-2-propyl-1,3-propanediol, and the like. It is done. The monobasic acid is not limited to the following, but monovalent fatty acids having 4 to 16 carbon atoms are mainly used. Specifically, butyric acid, valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, mysteric acid, palmitic acid, beef tallow fatty acid, stearic acid, caproleic acid, palmitoleic acid, petrothelin Examples include acids, oleic acid, elaidic acid, sorbic acid, linoleic acid, linolenic acid, ricinoleic acid and the like.

ここで、Ｒ³はアルキル基であり、同一分子中に２種以上の異なるアルキル基が混在してもよく、ｎは３〜１０の数であることが好ましい。具体的なＰＡＯとしては、以下のものに限定されるわけではないが、ポリブテン、ポリイソブチレン、１−デセンオリゴマーや、１−デセンとエチレンとのオリゴマー等を挙げることができる。 On the other hand, examples of PAO include olefins represented by the following formula:

Here, R ³ is an alkyl group, and two or more different alkyl groups may be mixed in the same molecule, and n is preferably a number of 3 to 10. Specific examples of the PAO include, but are not limited to, polybutene, polyisobutylene, 1-decene oligomer, and oligomer of 1-decene and ethylene.

  The above base oil can be mixed with other lubricating oils as necessary. In such a case, if 80% by weight or more of the total amount of the base oil is at least one selected from POE and PAO, the high temperature performance and various characteristics such as the low temperature pour point can be suitably used without substantially impairing.

  The thickener of the present invention is represented by lithium stearate, lithium 12-hydroxystearate (hereinafter referred to as “Li-12OHst”), and the following formulas I and II in consideration of the economical efficiency of the blending amount and shear stability. Using a compound selected from the group consisting of:

ここで、Ｒ¹およびＲ²は各々独立に、炭素数８〜１８の直鎖状のアルキル基を表す。

Here, R ¹ and R ² each independently represents a linear alkyl group having 8 to 18 carbon atoms.

  The blending amount of the thickener used in the present invention is such that the blending amount of the thickening agent is relative to the entire grease composition from the viewpoint of not increasing the stirring resistance of the grease composition, the torque of the linear motion device or the heat generation during sliding. And 10 to 17% by weight, more preferably 8 to 15% by weight. Further, the thickener having poor shear stability is easily softened during operation of the linear motion device and causes leakage of the grease composition. Furthermore, in the compounds represented by the above formulas I and II, if the alkyl group has less than 8 carbon atoms, the amount of thickener required to exhibit an appropriate consistency is too small, and the grease composition The shear stability of the will deteriorate. In addition, when the number of carbon atoms is extremely small, the affinity between urea and the base oil is attenuated, and there is a possibility that the thickening property of urea is lost. On the other hand, in the compounds represented by the above formulas I and II, if the alkyl group has 19 or more carbon atoms, the amount of the thickener increases and the torque performance and heat generation characteristics of the grease are deteriorated.

  In order to provide excellent wear resistance, the grease composition according to the present invention contains an extreme pressure additive. Specific examples of the extreme pressure additive include molybdenum dithiocarbamate (hereinafter referred to as “MoDTC”), molybdenum dithiophosphate (hereinafter referred to as “MoDTP”), thiophosphate, and the like. The compounding amount of the extreme pressure additive is 1 to 5% by weight with respect to the total amount of the grease composition. When the amount of the extreme pressure additive is 1% by weight or less, the effect of wear resistance cannot be obtained, and when it is 5% by weight or more, corrosion wear is caused.

  The blending degree of the grease composition according to the present invention is preferably 230 to 320. When the penetration is 230 or less, the grease composition becomes too hard and the torque at the start of the linear motion device becomes large. In addition, in a grease composition having a penetration of 230 or less, the fluidity of the grease itself is insufficient, and the life of the linear motion device is shortened. On the other hand, in a grease composition having a blending degree of 320 or more, the grease itself becomes too soft and does not stay on the sliding portion, and the life of the grease itself is also reduced.

  In addition, the grease composition according to the present invention may contain various additives as desired in order to improve various properties. For example, an antioxidant, a rust inhibitor, an oily agent, a metal deactivator, and the like can be added singly or in combination within a range that does not impair the effects of the present invention.

  Specific examples of the antioxidant include amine compounds such as phenyl-1-naphthylamine, phenol compounds such as 2,6-t-butylphenol, sulfur compounds, zinc dithiophosphate compounds, and the like. Specific examples of the rust inhibitor include organic sulfonates of alkali metals or alkaline earth metals, alkyl or alkenyl succinic acid derivatives such as alkyl or alkenyl succinic acid esters, and partial esters of polyhydric alcohols such as sorbitan monooleate. Etc. Furthermore, specific examples of the oil-based agent include fatty acids and animal and vegetable oils. Furthermore, a benzotriazole etc. can be mentioned as a specific example of a metal deactivator. In particular, the benzotriazole derivative is preferably added to the grease composition as a corrosion inhibitor against the discoloration and corrosion wear of the metal surface caused by the extreme pressure additive. In this case, the addition amount of the benzotriazole derivative is preferably 0.05 to 0.2% by weight with respect to the total amount of the grease composition.

  The present invention will be described in more detail with reference to the following examples and comparative examples of the present invention, but these are illustrative and the present invention is not limited to the following specific examples. Those skilled in the art can implement the present invention by making various modifications to the embodiments shown below, and such modifications are included in the scope of the claims of the present application.

The grease composition according to the present invention is enclosed in the ball screw device shown in FIG. 1 for actual use. Here, the composition and properties of the grease to be filled are varied for each of the examples and the comparative examples, and the durable life, torque, and the like of the ball screw device, which is a linear motion device, are measured and compared.
Test 1
An acceleration pickup was attached to the nut of the ball screw, and the operation time when the vibration value exceeded 12 mm ² / s was regarded as the durable life of the linear motion device. The durability test was performed under the conditions of a nut moving speed of 3 m / s, a load of 10 kg, and an ambient temperature of 140 ° C.
Test 2
Torque measurement was performed by measuring both the starting torque at the start and the dynamic torque at the steady operation under the operating conditions of a moving speed of 1 m / s, a load of 10 kg, and an ambient temperature of 25 ° C.
Test 3
The durability life was also evaluated when the ball screw was reciprocated at a frequency of 3 Hz and a screw rotation angle of ± 10 °. In this case, the load life was 10 kg, the ambient temperature was 140 ° C., and the operation time when the vibration value increased by 5 mm ² / s from the initial value was defined as the durable life.

  In the following description, the durable life obtained in the above-described test 1 and test 3 is defined as durable life 1 and durable life 2, respectively. A ball screw device having a light diameter of 15 mm and a lead of 10 mm was used as a durable specimen.

Next, examples according to the present invention and comparative examples will be described in detail.
FIG. 2 shows the results of endurance tests under the above test conditions for various extreme pressure additives and thickeners. From FIG. 2, the durability life 1 and the durability life 2 of the ball screw are shown as ratios to the durability life 1 and the durability life 2 of the comparative example 1 (Li-12OHst-POE composition, extreme pressure additive-free product), respectively. . From the results of Examples 1 to 6, by adding MoDTP, MoDTC, and thiophosphate as extreme pressure additives, the ball screw has a durability life of 2.5 times or more and a durability life 2 of 5 times or more. Was found to be feasible. Also, from the comparison of the results of Examples 1 and 7, it was also found that aliphatic diurea had a slightly longer durability life 1 and 2 than Li-12OHst. Furthermore, from the comparison of the results of Examples 8 and 9, it was also found that the diurea of the formula I is slightly more advantageous with respect to the durable lifetimes 1 and 2 than the diurea of the formula II.

  From the comparison of the results of Example 10 and Comparative Example 2, it can be seen that the compounding amount of the extreme pressure additive is preferably 1% by weight or more with respect to the total amount of the grease composition. On the other hand, the blending amount of the extreme pressure additive should be suppressed to 5% by weight or less. Even if the extreme pressure additive used in the present invention is added in an amount of 5% by weight or more, the effect corresponding to the added amount is not obtained. In addition, the sulfur-containing extreme pressure additive used in the present invention is susceptible to corrosion, and if added in a large amount, it may cause undesirable phenomena such as discoloration of the metal surface and corrosion wear. .

  In Examples 4 to 6, among the thiophosphates, an extreme pressure additive called triphenylphosphorothionate was used. The extreme pressure additive used in Example 4 is a type of additive in which no substituent is introduced into the phenyl group in the molecule. On the other hand, the extreme pressure additive used in Examples 5 and 6 is a type of extreme pressure additive in which an alkyl group is introduced into an intramolecular phenyl group.

  From the comparison of the results shown in Examples 4 to 6, the type of triphenyl phosphorothionate in which an alkyl group is introduced into a phenyl group is more durable than triphenyl phosphorothioate in which no alkyl group is introduced. 2 proved to be advantageous. This is because a type of triphenyl phosphorothionate in which an alkyl group is introduced into a phenyl group is superior in oil solubility to triphenyl phosphorothioate in which no alkyl group is introduced, and is easily guided to a sliding part efficiently. is there.

FIG. 3 shows the results of examining the lifespans 1 and 2 of the ball screw and the dynamic friction torque when the base oil kinematic viscosity of the grease composition shown in Example 1 was changed. In FIG. 3, when the base oil kinematic viscosity at 40 ° C. is 10 mm ² / s, the result in each test is shown as a ratio based on each measured value. As is clear from FIG. 3, the kinematic viscosity of the grease base oil having both durable life 1 and 2 and low torque performance is preferably 14 to 70 mm ² / s at 40 ° C., and 15 to 60 mm ² / s. It can be seen that it is more preferable. When the base oil kinematic viscosity exceeds 70 mm ² / s at 40 ° C., the endurance life 2 sharply decreases. This is presumed to be caused by the deterioration in the replenishability of the lubricating oil to the swinging sliding surface as the base oil viscosity increases. Further, when the base oil kinematic viscosity exceeds 70 mm ² / s, an increase in torque accompanying a base oil kinematic viscosity increase becomes significant. This is considered to be due to the significant increase in heat generation, but when the base oil kinematic viscosity exceeds 70 mm ² / s, the durability life 1 tends to decrease slightly.

FIG. 4 is a graph showing the relationship between the blending amount of the thickener, the dynamic friction torque, and the mixing stability. In the example shown in FIG. 4, PAO (Mobil Chemical Products, Mobil SHF 63) having a kinematic viscosity at 40 ° C. of 30 mm ² / s is used as a base oil, and a diurea represented by the chemical formula I is used as a thickener. And a grease composition containing a compound having a blending consistency of 280. In the results shown in FIG. 4, the dynamic friction torques of other blending amounts are shown as ratios based on the dynamic friction torque when the blending amount of the thickener is 10% by weight. As is clear from the results shown in FIG. 4, the blending amount of the thickener having both low torque performance and shear stability is preferably 10 to 17% by weight with respect to the total amount of the grease composition. found. More preferably, the amount of the thickener is 10 to 15% by weight.

1 is a cross-sectional view showing a ball screw device that is incorporated into a semiconductor or a liquid crystal manufacturing apparatus and used as an embodiment of a linear motion device according to the present invention. The result of having performed the durability test by this invention about various extreme pressure additives and thickeners is shown. In Fig. 2, PAO is a mixture of Mobil SHF41 and SHF63 manufactured by Mobil Chemical Products. Li-120HSt is S-7000 OH manufactured by Sakai Chemical Industry. The results of examining the lifespans 1 and 2 of the ball screw and the dynamic friction torque when the base oil kinematic viscosity of the grease composition shown in Example 1 was changed are shown. It is a figure which shows the relationship between the compounding quantity of a thickener, dynamic friction torque, and mixing stability in this invention. In the experiment shown in FIG. 4, 4% by weight of MoDTP (Sakura Loop 300) was added as an extreme pressure additive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ball screw shaft, 12 ... Ball screw groove, 20 ... Ball nut, 24 ... Ball screw groove, 30 ... Ball, 40 ... Tube type circulation path

Claims (3)

A base oil having a base oil dynamic viscosity of 14 to 70 mm ² / s at 40 ° C .;
A thickener comprising at least one selected from lithium stearate, lithium 12-hydroxystearate, diurea compounds represented by the following formulas I and II;
An extreme pressure additive containing at least one selected from molybdenum dithiophosphate, molybdenum dithiocarbamate and thiophosphate, and a grease composition comprising:
The blending amount of the thickener is 8 to 17% by weight with respect to the total amount of the grease composition, and the blending amount of the extreme pressure additive is 1 to 5% by weight with respect to the total amount of the grease composition. And the grease composition has a penetration degree of 230 to 320.

(Here, R ¹ and R ² each independently represents a linear alkyl group having 8 to 18 carbon atoms.)   The base oil contains at least one selected from polyol ester oil or poly α-olefin oil, and the polyol ester oil or poly α-olefin contains 80% by weight or more based on the total amount of the base oil, The grease composition according to claim 1. A linear motion device in which the grease composition according to claim 1 is enclosed.

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