JP2007271056A - Rolling bearing and bearing unit for actuators for hard disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing and bearing unit for actuators for hard disk drive which operate stably with low torque over a wide temperature range from very low temperature to high temperature with low outgassing and high durability. <P>SOLUTION: In the rolling bearing which is used for actuators swingably supporting a magnetic head of hard disk drive, characterized by fluorine polymers with the viscosity index of more than 300 being applied on at least one member in the inner ring raceway surface, outer ring raceway surface, rolling elements, and retainer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rolling bearing for an actuator of an HDD incorporated in an actuator (particularly a swing arm) which is a component of a hard disk drive device (hereinafter referred to as “HDD”), or an HDD in which the rolling bearing is accommodated in a housing and unitized. The present invention relates to a rolling bearing unit for an actuator.

  Recent HDDs have a higher recording density or higher precision, and the flying height is extremely narrow to 100 nm or less. In an HDD having such a small gap, the adhesion of foreign matter on the magnetic disk can be a fatal obstacle. For example, if the lubricant evaporated as outgas from the lubricant adheres to the magnetic disk surface, problems such as the magnetic disk and the magnetic head attracting each other and normal reading / writing cannot be performed. For this reason, it is desired that members used in the HDD have less chemical contamination.

  Against this background, the present applicant has previously proposed a rolling bearing for an actuator of an HDD using a fluorine-based lubricating oil (see Patent Document 1).

JP 2003-97573 A

  However, recently, car navigation systems with built-in HDDs and various mobile devices have become widespread, and the operating temperature of HDDs tends to spread to both the low temperature side and the high temperature side, which is better in a wider temperature range. New operating characteristics have been demanded. Although the outgas can be reduced by using the fluorine-based lubricating oil, further improvement is necessary to simultaneously realize the operating characteristics in a wider temperature range.

  The present invention has been made in view of such a situation, and operates for a HDD actuator that operates stably with low torque in a wider temperature range from extremely low temperature to high temperature, and has excellent durability with low outgas. It is to provide a bearing and a rolling bearing unit.

In order to solve the above-mentioned problems, the present invention provides the following rolling bearings and rolling bearing units for HDD actuators.
(1) In a rolling bearing of an actuator that swings and supports a magnetic head of a hard disk drive device, a fluoropolymer having a viscosity index of 300 or more is applied to at least one member of an inner ring raceway surface, an outer ring raceway surface, a rolling element, and a cage. Rolling bearing for actuator of hard disk drive device characterized by oiling.
(2) The rolling bearing for an actuator of a hard disk drive device according to (1), wherein the fluoropolymer is a linear perfluoropolyether.
(3) A rolling bearing unit for an actuator of a hard disk drive device, wherein the rolling bearing for an actuator according to the above (1) or (2) is accommodated in a housing.

  According to the present invention, since it is lubricated by a fluorine-containing polymer having a specific viscosity index, the generation of outgas is suppressed, and from a very low temperature to a high temperature, specifically from a very low temperature of −40 ° C. to a high temperature of 100 ° C., Provided are a rolling bearing and a bearing unit for an HDD actuator having low torque and low torque fluctuation, which have not been obtained so far, and having high performance and high reliability.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  The rolling bearing for actuator of the HDD of the present invention (hereinafter simply referred to as “rolling bearing”) is not limited in its configuration. For example, as shown in FIG. 1, an inner ring 2 having an inner ring raceway 1 on its outer peripheral surface, The outer ring 4 having the outer ring raceway 3 is arranged concentrically on the inner peripheral surface, and a plurality of balls 5 are provided between the inner ring raceway 1 and the outer ring raceway 3 by a cage 7 so as to be freely rollable. 4 is sealed with a sealing member 6. Then, at least one member of each raceway surface of the inner ring raceway 1 and the outer ring raceway 3, the balls 5 and the cage 7 is coated with the following fluoropolymer. Such a lubrication system has the advantage of lower torque than grease lubrication.

  The fluorine-containing polymer is not limited as long as its viscosity index is 300 or more. When the viscosity index is 300 or more, the change in kinematic viscosity in the temperature range of −40 ° C. to 100 ° C. can be kept small. Therefore, kinematic viscosity hardly increases even at an extremely low temperature of −40 ° C., an oil film is secured even at a high temperature of 100 ° C., and it becomes possible to reduce torque and torque fluctuation while maintaining durability performance required as an actuator for HDD. .

Since the fluorine-containing polymer preferably has a higher viscosity index, it is preferable to use a perfluoropolyether (PFPE) polymer and a derivative thereof, for example,
-C _X F _2X -O- (X is an integer of 1 to 4)
And a polymer having a main structural unit. Moreover, what has the following side chain structure (A) or linear structure (B) can be mentioned as a derivative | guide_body of PFPE.

  Among them, PFPE having a straight chain structure is preferable because it has a high viscosity index and a low pour point, and therefore, good lubricating characteristics can be obtained in a wide temperature range and the evaporation characteristics are also excellent.

  Such PFPE is also available from the market. For example, DUPONT's Krytox 143, Krytox GPL, Krytox 1500, AUSIMNT's Fomblin Y Standard, NOK Kryuber's Barrierta J Fluid, As the chain structure product, for example, demnum of Daikin Industries, Fomblin Z of AUSIMNT, UNIFOR of Nye, etc. can be suitably used. These PFPEs can be used singly or in combination, or in combination with other PFPE having a viscosity index exceeding 300.

Further, the kinematic viscosity of the fluoropolymer is preferably ^{50~150mm 2 / s (40 ℃)} , 50mm 2 / s poor durability at (40 ° C.) ^{below, 150mm 2 / s (40 ℃} ) If it exceeds, torque will increase.

  The application amount of the fluoropolymer is preferably 0.1% to 10% of the bearing internal space volume formed by the inner ring 2, the outer ring 4 and the balls 5. Furthermore, considering wear resistance (fretting resistance) and lubricating oil leakage, 0.25% to 5% is preferable. In particular, when the upper limit is exceeded, it is impossible to reduce the torque. Although the application method is not limited, a prescribed amount of fluoropolymer is measured by a micro syringe or plunger pump capable of measuring a very small amount, and the inner ring 2, the outer ring 4, the ball 5, and the cage 7 are assembled. A method of discharging to the surface and rotating the bearing several times is preferable. In order to prevent leakage of the fluoropolymer, it is preferable to apply the fluoropolymer as a thin film. In this case, the bearing is immersed in a solution obtained by diluting the fluoropolymer in a solvent and adheres to the outer surface. The solution thus obtained may be wiped off and dried. Moreover, the wiping operation | work can be skipped by drying after discharging this solution on a rolling element.

  Moreover, the rolling bearing of this invention can also be unitized. FIG. 2 is a cross-sectional view showing an example of the bearing unit. A pair of rolling bearings 8 of the present invention can be used, and an outer ring can be mounted on the housing 9 and an inner ring can be mounted on the shaft 10 to form a bearing unit.

Hereinafter, the present invention will be clarified by examples and comparative examples.
(Examples 1-2, Comparative Examples 1-5)
The fluoropolymer shown in Table 1 and other lubricating oil or grease were sealed so as to occupy 3% of the bearing internal space volume of a rolling bearing “MR7422 (outer diameter 7 mm, inner diameter 4 mm, width 2 mm)” manufactured by NSK. Two bearings were housed in a housing as shown in FIG. 2 to produce a bearing unit. Each bearing unit was subjected to the following (1) torque evaluation test, (2) outgas test, and (3) swing durability test.

(1) Torque evaluation test While rotating the bearing unit at a rotation speed of 2 rpm, the ambient temperature was continuously raised from -30 ° C to 100 ° C, and the dynamic torque (average value) at that time was measured. The measurement results are shown in FIG. 3 and were accepted when the ambient temperature was 1 mN · cm or less at any ambient temperature.

(2) Outgas test The amount of gas generated when the bearing unit was heated at 100 ° C. for 1 hour was analyzed by a mass spectrometry gas chromatograph (GCMS), and the total amount of hydrocarbon generated (decane conversion) was measured. The results are shown in Table 1 as relative values with the value of the synthetic oil-mineral oil urea grease of Comparative Example 5 being 1, but 0.3 or less was accepted.

(3) Swing durability evaluation Observing torque fluctuation of bearing unit over time under conditions of rocking angle of 16 °, frequency of 100Hz, preload (Fa) of 3N, and ambient temperature of 90 ° C. Number of times. 20 million times or more was accepted. In addition, when torque fluctuation did not occur at the time of 20 million times, the test was stopped there. The results are shown in Table 1.

  From the above test results, it can be seen that by using PFPE having a viscosity index of 300 or more, torque and torque fluctuation are small, outgas is small, and durability is excellent. Even in the case of PFPE as in Comparative Example 2 and Comparative Example 3, if the viscosity index is less than 300, torque reduction at low temperature cannot be realized.

It is sectional drawing which shows an example of the rolling bearing for actuators of HDD of this invention. It is sectional drawing which shows an example of the rolling bearing unit for actuators of HDD. It is a graph which shows the relationship between the temperature and dynamic torque which were obtained in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring raceway 2 Inner ring 3 Outer ring raceway 4 Outer ring 5 Ball 6 Seal member 7 Cage 8 Rolling bearing 9 Housing 10 Shaft

Claims (3)

  In a rolling bearing of an actuator that swings and supports a magnetic head of a hard disk drive device, a fluorine-containing polymer having a viscosity index of 300 or more is applied to at least one member of an inner ring raceway surface, an outer ring raceway surface, a rolling element, and a cage. A rolling bearing for an actuator of a hard disk drive device.   The rolling bearing for an actuator of a hard disk drive device according to claim 1, wherein the fluoropolymer is a linear perfluoropolyether. A rolling bearing unit for an actuator of a hard disk drive device, wherein the rolling bearing for an actuator according to claim 1 or 2 is accommodated in a housing.

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