JP2007170431A - Rolling bearing for hard disc drive actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing for a HDD actuator, having further lower torque, torque fluctuation and outgas. <P>SOLUTION: The rolling bearing for the hard disc drive actuator bears a magnetic head of the hard disc drive. It is filled with synthetic lubricating oil whose vapor pressure is 10<SP>-5</SP>Pa or lower at 25°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling bearing incorporated in a reciprocating rocking motion portion of an actuator (particularly a swing arm) that is a part of a component of a hard disk drive (hereinafter referred to as “HDD”).

  In a conventional HDD, the gap (flying height) between the magnetic head unit and the magnetic disk is set to be wide to some extent, so even if a small amount of foreign matter adheres to the magnetic disk, it is caused by contact between the magnetic head unit and the foreign matter. The fatal failure to do was difficult to occur. Therefore, in lubricants used in HDD bearings, improvement of lubrication performance (long-term acoustic performance) is a top priority, and low outgas performance is not considered as important as improvement of lubrication performance. It was.

  However, in recent HDDs, higher recording density and higher accuracy have progressed, and the flying height is often 100 nm or less. In such HDDs having such a small gap, foreign matter does not adhere to the magnetic disk. It can be a fatal obstacle. For example, when lubricating oil adheres to the magnetic disk, problems such as adsorption between the magnetic disk and the magnetic head, or “fluctuation” due to the adhering lubricating oil, and normal reading / writing cannot be performed. Therefore, since the member used in the HDD is required to generate less gas that causes adhesion of foreign matters, a member with less chemical contamination is desired. In particular, the demand for low outgassing for bearings in which a lubricant is sealed has become stricter year by year.

  In addition, because the actuator unit is arranged very close to the magnetic disk due to the structure of the HDD, it is easily heated by the heat generated by the voice coil motor, and unlike the spindle motor unit, a magnetic fluid seal or labyrinth that traps outgas. Does not have a maze structure. Therefore, the actuator unit is required to be more strictly outgassed.

  In view of such a situation, the present applicant has previously proposed a rolling bearing for an actuator of an HDD in which grease containing a fluorine-based lubricating oil is enclosed (see Patent Document 1).

JP 2003-97573 A

  As the HDD becomes thinner, the output of the voice coil motor is decreasing, and in order to cope with this, a reduction in torque of the bearing is required. Further, it is preferable that the torque fluctuation is as small as possible in the high-precision read / write operation in the HDD. However, in the lubrication system using grease, torque fluctuation is likely to occur due to the catching phenomenon of grease. In order to suppress a decrease in torque and torque fluctuation, the lubrication method using the lubricating oil is more advantageous than the lubrication method using the grease, but there is a problem that the lubricant is more likely to evaporate than when the lubricant is evaporated from the grease.

  The demand for higher performance of the HDD is inevitable, and an object of the present invention is to provide a rolling bearing for an actuator of the HDD that further promotes low torque, low torque fluctuation, and low outgas.

In order to achieve the above object, the present invention provides the following rolling bearing for an actuator of an HDD.
(1) A rolling bearing for an actuator for an HDD, wherein a synthetic lubricating oil having a vapor pressure of 10 ⁻⁵ Pa or less at 25 ° C. is enclosed in the rolling bearing for an actuator that supports the magnetic head of the HDD.
(2) The rolling bearing for an actuator of the HDD according to (1), wherein the synthetic lubricating oil is an ester-based synthetic lubricating oil having a kinematic viscosity at 40 ° C. of 30 to 150 mm ² / s.

The rolling bearing for the actuator of the HDD of the present invention adopts a lubrication system using synthetic lubricating oil, thereby achieving low torque and low torque fluctuation as compared with a lubrication system using grease, and a low of 10 ⁻⁵ Pa (25 ° C.) or less. Using synthetic lubricating oil with vapor pressure to reduce outgassing than before.

  Hereinafter, the rolling bearing for actuator of HDD of this invention is demonstrated in detail.

  The structure of the rolling bearing for the actuator of the HDD of the present invention is not particularly limited, and for example, a ball bearing shown in a sectional view in FIG. 1 can be exemplified. As shown in the drawing, an inner ring 2 having an inner ring raceway surface 1 on an outer peripheral surface and an outer ring 4 having an outer ring raceway surface 3 on an inner peripheral surface are arranged concentrically, and between the inner ring raceway surface 1 and the outer ring raceway surface 3. In addition, a plurality of balls 5 as rolling elements are rotatably held by a cage 7 and sealed by a seal member 6 so as to be generally configured. In addition, although illustration is abbreviate | omitted, it can also be set as the structure which united such a bearing integrally with the housing. And in this invention, the synthetic lubricating oil shown below is enclosed for lubrication.

Synthetic lubricants have excellent lubrication performance and have a vapor pressure of 10 ⁻⁵ Pa (25 ° C.) or less, but there are no restrictions on the type, but wettability with metals is high, lubricity and durability. Therefore, polyol ester oil, synthetic hydrocarbon oil, alkyl chain-derived polyphenyl ether oil, aromatic ester oil, and alkyl chain-derived naphthalene oil are preferable.

  The synthetic lubricating oil may be a commercially available product, for example, “NYETORR 5101” manufactured by NYE LUBRICATS as a polyol ester oil, “NYE2001” manufactured by NYE LUBRICATS as a synthetic hydrocarbon oil, etc. As polyphenyl ether oil, “Neobak SY”, “Neobak SX”, “LB-15”, “LB-100”, “S-3101”, “S-3101” and “S-” manufactured by Matsumura Oil Research Co., Ltd. 3230 ", etc., such as" TOTM "manufactured by Daihachi Chemical Industry Co., Ltd. as an aromatic ester oil," Lion diffusion pump oil S "manufactured by Lion Corporation as an alkyl chain-derived naphthalene oil, and" Lion diffusion pump oil A " Can be obtained.

  Among the above synthetic lubricating oils, ester-based synthetic lubricating oils are preferable because of excellent heat resistance and the like. Moreover, you may use said synthetic lubricating oil in mixture of 2 or more types.

The vapor pressure of the synthetic lubricating oil is more preferably 10 ⁻⁶ Pa (25 ° C.) or less. However, a synthetic lubricating oil having a vapor pressure of 10 ⁻¹² Pa (25 ° C.) or less has a high viscosity and it is difficult to satisfy low torque at the same time.

Moreover, it is preferable that said synthetic lubricating oil has kinematic viscosity of 30 mm < ² > / s (40 degreeC) or more. If the kinematic viscosity is less than 30 mm ² / s (40 ° C.), the formation of the oil film is not sufficient, and the durability may be insufficient. The upper limit of the kinematic viscosity is 150 mm ² / s in consideration of handleability, oil film formation, torque, and the like. In consideration of sufficient fretting wear resistance, the kinematic viscosity is more preferably 30 to 100 mm ² / s (40 ° C.). In addition, when mixing and using synthetic hydrocarbon oil, it is necessary to adjust so that it may become such kinematic viscosity as mixed oil.

  Additives can be added to the above synthetic lubricating oil to improve various characteristics. For example, rust preventives and antioxidants may be added for the purpose of improving lubrication durability, and boundary lubrication. An antiwear agent or an extreme pressure agent can be added for the purpose of preventing underwear. However, the addition amount of these additives must be in a range that does not induce an increase in vapor pressure and does not cause chemical contamination, and is preferably less than 3% by mass in total.

  The amount of the synthetic lubricating oil to be enclosed is preferably 0.1 to 10% of the bearing internal space volume, and more preferably 0.25 to 5% in consideration of bearing life and lubricating oil leakage. As a sealing method, a specified amount is measured with a micro syringe or pump that can measure a very small amount of synthetic lubricating oil, and the inner ring, outer ring, rolling element, and cage are assembled and discharged onto the rolling element, and the bearing is rotated several times. The method is preferred. In order to prevent leakage of the lubricating oil, when the synthetic lubricating oil is coated as a thin film, the bearing may be immersed in a diluted lubricating oil obtained by diluting the synthetic lubricating oil with a solvent. Furthermore, in order to avoid adhesion of the lubricant to the outside of the bearing, the lubricant may be dried after being discharged into the bearing or on the rolling elements.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereby.

[Examples 1-2, Comparative Examples 1-3]
Single row deep groove ball bearings with non-contact steel seal (“695ZZ” manufactured by NSK Ltd., inner diameter 5 mm, outer diameter 13 mm, width 4 mm) are all commercially available pentaerythritol ester oil (PET), aromatic ester oil ( AE), alkyl diphenyl ether oil (ADE), poly α-olefin oil (PAO), or mineral oil (MO) was sealed so as to be 3% of the bearing internal space volume to produce a test bearing. The test bearing was heated in a container at 100 ° C. for 1 hour, and the amount of gas generated was measured by a head space mass spectrometry gas chromatograph (GCMS). The results are shown in Table 1, and a level that does not possibly contaminate the disk surface of the HDD when used for a long time is set as pass, and a mark “X” is set as a fail level.

From Table 1, it can be seen that by enclosing a synthetic lubricating oil having a vapor pressure of 10 ⁻⁵ Pa (25 ° C.) or less, the generation of outgas can be suppressed to a level that causes no problem in practice.

[Examples 3-4, Comparative Examples 4-6]
Nippon Seiko Co., Ltd. “B4-47” (outer diameter 7 mm, inner diameter 4 mm, width 2 mm, with single seal) is used as a test bearing in pairs, and the lubricating oil shown in Table 2 is 3% of the bearing internal space volume. It enclosed so that it might become. In the table, DPET is dipentaerythritol ester oil, and PFPE is perfluoropolyether oil, both of which are commercially available. PET, AE and ADE are as described above. And about the test bearing, the torque was measured using the torque measuring apparatus shown in FIG. In the illustrated torque measuring apparatus, the test bearings 11 and 11 are mounted on the housing 12 in a pair of upper and lower sides. A motor 13 is attached to one end of the housing 12, and a swing arm 14 is attached to the other end, and a non-contact displacement meter 15 is disposed at the tip of the swing arm 14 so as to face the target 16. The non-contact displacement meter 15 is fixed on the surface of the rotary stage 17, and the rotary stage 17 is reciprocated in the circumferential direction by the rotary stage driver 18, and the swing arm 14 performs a seek equivalent operation 19. The motor 13 is connected to a non-contact displacement meter 15 via a driver 20, and a drive current 21 corresponding to the tracking equivalent operation amount 14 is measured by the personal computer 22. Here, rocking was performed 10 ⁸ times at room temperature at a rocking angle of 8 °, a frequency of 90 Hz, and an axial load of 2N. The results are shown in Table 2, but the rate of increase in the average torque fluctuation range after the test is 5% or less with respect to the initial torque fluctuation average value, and “○” is marked, and over 5% is rejected with “×”. Was written.

It can be seen from Table 2 that torque fluctuations can be suppressed by enclosing a synthetic lubricating oil having a vapor pressure of 10 ⁻⁵ Pa (25 ° C.) or less.

[Torque evaluation test]
Using the PET and AE, the mixing ratio of the two was changed and mixed so as to obtain a predetermined kinematic viscosity to prepare a test lubricating oil. Single row deep groove ball bearing with non-contact steel seal (“B8Z-42” manufactured by NSK Ltd., inner diameter 7.94 mm, outer diameter 12.7 mm, width 3.97 mm) A test bearing was manufactured by enclosing it to 3%. And the inner ring | wheel was rotated at 2 rpm with the rotating apparatus in the state which loaded the axial load of 9.8N, and the torque required for the rotation initial stage was measured. For comparison, the same measurement was performed with a commercially available urea grease enclosed. The results are shown in FIG. 3 as a torque ratio where the torque of the urea grease is 1, and this torque ratio of 0.5 or less was accepted.

As shown in FIG. 3, it can be seen that if the kinematic viscosity is 150 mm ² / s (25 ° C.) or less, low torque that is considered to be practically good can be realized.

It is sectional drawing which shows one Embodiment of the rolling bearing for actuators of the HDD of this invention. It is the schematic which shows a torque measuring device. It is a graph which shows the relationship between kinematic viscosity of the lubricating oil and torque which were obtained in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring raceway surface 2 Inner ring 3 Outer ring raceway surface 4 Outer ring 5 Ball 6 Seal member 7 Cage

Claims (2)

In rolling bearings for actuators that support magnetic heads of hard disk drives,
A rolling bearing for an actuator of a hard disk drive, wherein a synthetic lubricating oil having a vapor pressure at 25 ° C. of 10 ⁻⁵ Pa or less is enclosed. The rolling bearing for an actuator of a hard disk drive according to claim 1, wherein the synthetic lubricating oil is an ester-based synthetic lubricating oil having a kinematic viscosity at 40 ° C of 30 to 150 mm ² / s.

Images