JPH09274766A - Damping material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent production of read-write errors and to suppress generation of noise due to vibration of a chassis itself by forming a damping material from a viscoelastic material comprising an acryl adhesive. SOLUTION: The damping material 7 is assembled between a spindle motor 3 of a magnetic disk device and a chassis 6 which houses the motor, and is made of a viscoelastic material comprising an acryl adhesive. Thereby, the vibration energy generated by the spindle motor 3 can be transduced into thermal energy. As a result, propagation of vibration from the motor to a magnetic disk or a magnetic head can be decreased or removed, and generation of read- write errors can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a damping material used in magnetic disk devices such as hard disk drives and magneto-optical disk drives.

[0002]

2. Description of the Related Art In a magnetic disk drive for rotating a recording disk such as a hard disk drive or a magneto-optical disk drive, a particularly small magnetic disk drive generally has a plurality of magnetic disks as shown in a schematic sectional view of FIG. 1, a magnetic head 2 for reading and writing information from the magnetic disk 1, a spindle motor 13 for rotating the magnetic disk 1, and a voice coil motor 4
The voice coil motor 4 and the actuator 5 that interposes the magnetic head 2 are housed in a sealed case 6.

[0003]

However, recent magnetic disk devices tend to be smaller and lighter, and the number of revolutions of the spindle motor 13 tends to increase as the access time is shortened. Therefore, the vibration generated from the spindle motor 13 is easily transmitted to the magnetic disk 1 and the magnetic head 2, which causes a problem such as a read / write error. Further, the vibration generated from the spindle motor 13 is transmitted to the housing 6, and the housing 6 is likely to resonate, which causes a problem of noise due to the vibration of the housing 6 itself.

The present invention has been made in view of such circumstances, and provides a damping material capable of preventing the occurrence of a read / write error and solving the problem of noise due to the vibration of the housing itself. To that end.

[0005]

In order to achieve the above object, a damping material of the present invention is a damping material arranged between a spindle motor of a magnetic disk device and a housing for housing the spindle motor. The damping material is formed of a viscoelastic body made of an acrylic adhesive.

That is, the inventors of the present invention obtain a damping material for a magnetic disk device capable of reducing or eliminating vibrations from a spindle motor to a magnetic disk or a magnetic head and vibrations from a spindle motor to a housing. Therefore, a series of studies were repeated. In the process of that research, we focused on a viscoelastic body made of an acrylic adhesive that has excellent heat resistance and vibration damping properties, and this viscoelastic body easily deforms due to vibration and produces internal resistance (molecular friction). Therefore, we have found that it is possible to convert vibration energy into heat energy. As a result of further research, if a vibration damping material formed of a viscoelastic body made of the acrylic adhesive is disposed between the spindle motor of the magnetic disk device and the housing that houses it. Since it is possible to reduce or eliminate the vibration from the spindle motor to the magnetic disk or the magnetic head, it is possible to prevent the occurrence of a read / write error and to reduce or eliminate the vibration from the spindle motor to the housing. The inventors have found that the problem of noise due to vibration of the housing itself can be solved, and have reached the present invention.

Further, if the acrylic adhesive is crosslinked so that the gel fraction (degree of crosslinking) is 90% or more, the amount of generated gas will be no problem when used as a vibration damping material.
It has been found that the magnetic disk is prevented from being contaminated and is most suitable as a damping material for a closed magnetic disk device.

[0008]

Next, embodiments of the present invention will be described in detail.

The vibration damping material of the present invention is formed of a viscoelastic body made of an acrylic adhesive, and as shown in the schematic sectional view of FIG. It is arranged by wearing. Examples of this disposing method include a method of sticking by viscoelastic body's viscosity, a method of sandwiching between the spindle motor 3 and the housing 6, and the like.

As the acrylic pressure-sensitive adhesive, for example,
Examples thereof include those obtained by the method disclosed in JP-A-5-132658. This method is a mixture of an acrylic acid alkyl ester monomer and a monomer having a carboxyl group, a photopolymerization initiator such as 1-hydroxycyclohexyl phenyl ketone, trimethylolpropane triacrylate, ethylene glycol diacrylate, pentaerythritol acrylate, This is a method of obtaining a tape-shaped adhesive by mixing a crosslinking agent such as tetramethylolmethane tetraacrylate and irradiating with ultraviolet rays. As the acrylic acid alkyl ester, those having an alkyl group having 8 to 12 carbon atoms are used, and specifically, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, etc. Can be given.

The acrylic pressure-sensitive adhesive used in the present invention is preferably crosslinked so that the gel fraction is 90% or more. That is, if the gel fraction is less than 90%, the presence of uncrosslinked polymer and residual monomer
This is because the amount of generated gas increases at high temperatures, and the generated gas may contaminate the magnetic disk. Among them, it is preferable to crosslink so that the gel fraction of the acrylic pressure-sensitive adhesive is 95% or more, and particularly, the gel fraction is 10%.
0% is more preferable.

The gel fraction (degree of crosslinking) is calculated by the following procedure. That is, first, a test piece (about 0.1
After the weight (W ₁ ) of g) was measured, this was put into 45 ml of isopropyl alcohol (IPA) and immersed at room temperature for 7 days (168 hours). At this time, the non-gelled portion is dissolved in IPA. And insoluble matter 120
After drying at ± 5 ° C for 2 hours, the weight (W ₂ ) of the residue (gelled product) is measured, and the gel fraction is calculated based on the following mathematical formula. This is performed for five test pieces, and the average value is obtained.

[0013]

## EQU1 ## Gel fraction (%) = (W ₂ / W ₁ ) × 100

If the vibration damping material is formed of a viscoelastic body made of an acrylic adhesive, even if the viscoelastic body is a single layer body made of only one layer of the acrylic adhesive, There is no particular limitation, even if it is a laminated body formed by laminating two or more layers of the adhesive.

When the viscoelastic body is a laminated body,
The gel fraction of the acrylic pressure-sensitive adhesive forming each layer is preferably 90% or more. That is, if any one of the layers constituting the laminate includes a layer in which the gel fraction of the acrylic pressure-sensitive adhesive is less than 90%, the amount of gas generated from that layer may increase. This is because the generated gas may contaminate the magnetic disk. The viscoelastic body has a gel fraction of 9
Since it is easy to crosslink the acrylic pressure-sensitive adhesive so as to be 0% or more, it is preferable to form the laminate.

The thickness of the viscoelastic body is not particularly limited and is appropriately set depending on the rotational speed and size of the spindle motor, the size of the magnetic disk device, etc., but is usually about 50 μm to 4 mm. is there. Therefore, when the viscoelastic body is a monolayer body, the thickness of the monolayer body becomes the thickness of the viscoelastic body as it is. Further, when the viscoelastic body is a laminated body, the thickness of the viscoelastic body is the total thickness of the acrylic pressure-sensitive adhesive forming each layer. In this case, the thickness of the acrylic pressure-sensitive adhesive forming each layer is 20 to
It is preferable to set it in the range of 250 μm. That is, the thickness of the acrylic pressure-sensitive adhesive forming each layer is 20
If it is less than μm, a large number of acrylic pressure-sensitive adhesives must be laminated in order to laminate the entire viscoelastic body to a predetermined thickness, and it takes a long time and the workability is deteriorated.
On the contrary, the thickness of the acrylic adhesive that constitutes each layer is 250μ.
This is because if it exceeds m, it becomes difficult to crosslink so as to obtain a predetermined gel fraction (90% or more), and the amount of generated gas may increase. Above all, it is particularly preferable to set the thickness of the acrylic pressure-sensitive adhesive forming each layer to be in the range of 50 to 125 μm in terms of stacking workability, crosslinkability, and the like. Therefore, when the viscoelastic body is a laminated body, the number of laminated acrylic adhesives is appropriately set in consideration of the rotational speed and size of the spindle motor, the size of the magnetic disk device, and the like. .

Although FIG. 1 shows an example in which the damping material 7 is arranged between the lower end of the spindle motor 3 and the housing 6, the damping material 7 can be arranged at any position. The present invention is not limited to that shown in FIG. 1. For example, it may be arranged in the gap between the upper end of the spindle motor 3 and the housing 6 by pasting or the like. When the damping material 7 is provided at the lower end and the upper end of the spindle motor 3, respectively, vibration from the spindle motor 3 to the magnetic disk 1 or the magnetic head 2 and from the spindle motor 3 to the housing 6 This is particularly preferable because the vibration of is further reduced.

The vibration damping material of the present invention can be manufactured, for example, as follows. That is, a viscous material is prepared by mixing the acrylic pressure-sensitive adhesive forming material. A cross-linking agent such as trimethylolpropane triacrylate is added to the obtained viscous material, and this is coated on a release liner so as to have a predetermined thickness. Then, this is cross-linked by irradiation with ultraviolet rays or the like to obtain a tape-shaped adhesive. While the tape-shaped pressure-sensitive adhesive is peeled off from the release liner, the tape-shaped pressure-sensitive adhesive is wound into a roll to obtain a laminate. Then, the desired damping material can be manufactured by punching into a predetermined shape.

The method of laminating the acrylic pressure-sensitive adhesive is not particularly limited to the above-mentioned method, and other than the above, for example, a tape-shaped pressure-sensitive adhesive is cut into a size easy to bond and a rubber roll is used. There is a method of pasting together. And among these methods,
From the viewpoint of good workability and productivity, a method is preferred in which the tape-shaped pressure-sensitive adhesive is wound on a roll and laminated while being peeled from the release liner.

Next, an embodiment will be described.

[0021]

Example 1 90 parts by weight of isooctyl acrylate (hereinafter abbreviated as “part”) and 10 parts of acrylic acid were mixed in a nitrogen atmosphere, and 0.1 part of 1-hydroxycyclohexyl phenyl ketone was used as a photopolymerization initiator. In addition, irradiation with ultraviolet rays of 100 mj / cm ² was performed with a high pressure mercury lamp. To the obtained viscous material, 0.2 part of trimethylolpropane triacrylate was added as a cross-linking agent, and this was coated on a release liner so as to have a thickness of 125 μm. Further, cover this with a release liner, and use a high-pressure mercury lamp for 1400 mj.
/ Cm ² ultraviolet irradiation was performed to obtain a tape-shaped pressure-sensitive adhesive.
The gel fraction (degree of crosslinking) of this tape-like pressure-sensitive adhesive was calculated according to the procedure described above, and was found to be 92%. Then, while the tape-shaped adhesive having a thickness of 125 μm was peeled off from the release liner, it was wound 16 times around a roll having a diameter of 300 mm to obtain a laminate having a thickness of 2 mm. Furthermore, a release liner was attached to both sides of the obtained laminate, and about 1
A sheet having a size of 00 cm × 30 cm was obtained. This was punched into a 2 cm square piece using a Thomson die to obtain the desired damping material.

[0022]

Example 2 90 parts of isooctyl acrylate and 10 parts of acrylic acid were mixed in a nitrogen atmosphere, and 1-hydroxycyclohexyl phenyl ketone 0.1 was used as a polymerization initiator.
Then, 100 mj / cm ² of ultraviolet rays were irradiated with a high pressure mercury lamp. 0.2 parts of trimethylolpropane triacrylate as a crosslinking agent was added to the obtained viscous material,
This was coated on a release liner so as to have a thickness of 250 μm. Further, this was covered with a release liner and irradiated with ultraviolet rays of 1400 mj / cm ² with a high pressure mercury lamp to obtain a tape-shaped adhesive having a gel fraction of 90%. And
The tape-shaped adhesive having a thickness of 250 μm was wound around a roll having a diameter of 300 mm for 8 rounds while peeling from the release liner to obtain a laminate having a thickness of 2 mm. Otherwise, Example 1
The target vibration damping material was obtained in the same manner as in.

[0023]

Example 3 90 parts of isooctyl acrylate and 10 parts of acrylic acid were mixed in a nitrogen atmosphere to give 1-hydroxycyclohexyl phenyl ketone 0.1 as a polymerization initiator.
Then, 100 mj / cm ² of ultraviolet rays were irradiated with a high pressure mercury lamp. 0.2 parts of trimethylolpropane triacrylate as a crosslinking agent was added to the obtained viscous material,
This was coated on a release liner so as to have a thickness of 50 μm. Further, cover this with a release liner, irradiate with ultraviolet rays of 1400 mj / cm ² with a high pressure mercury lamp,
A tape-like pressure-sensitive adhesive having a gel fraction of 95% was obtained. Then, while peeling the tape-shaped adhesive having a thickness of 50 μm from the release liner, it is wound around a roll having a diameter of 300 mm for 40 turns.
A laminated body having a thickness of 2 mm was obtained. Other than that, the target damping material was obtained in the same manner as in Example 1.

[0024]

Example 4 90 parts of isooctyl acrylate and 10 parts of acrylic acid were mixed in a nitrogen atmosphere to give 0.1-hydroxycyclohexyl phenyl ketone 0.1 as a polymerization initiator.
Then, 100 mj / cm ² of ultraviolet rays were irradiated with a high pressure mercury lamp. 0.2 parts of trimethylolpropane triacrylate as a crosslinking agent was added to the obtained viscous material,
This was coated on a release liner so as to have a thickness of 2 mm. Further, this was covered with a release liner and irradiated with ultraviolet rays of 1400 mj / cm ² by a high pressure mercury lamp to obtain a tape-shaped adhesive having a gel fraction (degree of crosslinking) of 85%. Then, release liners were attached to both surfaces of the obtained tape-like pressure-sensitive adhesive to obtain a sheet having a size of about 100 cm × 30 cm.
Other than that, the target damping material was obtained in the same manner as in Example 1.

[0025]

Example 5 90 parts of isooctyl acrylate and 10 parts of acrylic acid were mixed in a nitrogen atmosphere, and 1-hydroxycyclohexyl phenyl ketone 0.1 was used as a polymerization initiator.
Then, 100 mj / cm ² of ultraviolet rays were irradiated with a high pressure mercury lamp. 0.2 parts of trimethylolpropane triacrylate as a crosslinking agent was added to the obtained viscous material,
This was coated on a release liner so as to have a thickness of 1 mm. Further, this was covered with a release liner and irradiated with ultraviolet rays of 1400 mj / cm ² with a high pressure mercury lamp to obtain a tape-shaped adhesive having a gel fraction (degree of crosslinking) of 88%. Then, while peeling the tape-shaped adhesive having a thickness of 1 mm from the release liner, the tape-shaped adhesive was wound twice around a roll having a diameter of 300 mm to obtain a laminate having a thickness of 2 mm. Otherwise, Example 1
The target vibration damping material was obtained in the same manner as in.

Using the products of Examples 1 to 5 thus obtained, evaluation tests were carried out on the vibration damping characteristics and the amount of generated gas according to the following criteria. The results are also shown in Table 1 below.

[Damping characteristics] A SUS foil having a thickness of 50 μm is attached to one surface of the damping material obtained in each of the above examples, and a base material (SPCC) having a thickness of 500 μm is attached to the other surface. A sample was prepared. The obtained sample was left in a constant temperature bath set at 60 ° C., a vibration of a frequency of 5 kHz was applied by an exciter, and the loss coefficient was determined by the half width method. It should be noted that if the loss coefficient is 0.05 or more, it has practical damping characteristics, and it can be said that the object of the present invention has been achieved.

[Amount of Generated Gas] Using gas chromatography (Shimadzu QP-1000, manufactured by Shimadzu Corporation), 1
Heat treatment was performed at 30 ° C. for 30 minutes, and quantitative analysis was performed.

[0029]

[Table 1]

As is clear from the results shown in Table 1, it was confirmed that all the products of Examples had loss coefficients of 0.05 or more, and had practical vibration damping characteristics. Also,
The products of all the examples produced a small amount of gas, and the gel fraction was 90% in particular.
In the products of Examples 1 to 3 using the acrylic pressure-sensitive adhesive cross-linked so that the amount thereof is not less than 100%, the amount of generated gas is further smaller, so that the contamination of the magnetic disk can be suppressed to a minimum, and particularly the sealed magnetic Suitable as a damping material for disk devices.

[0031]

As described above, the damping material of the present invention is disposed between the spindle motor of the magnetic disk device and the housing that houses it, and moreover, it is a viscoelastic material made of an acrylic adhesive. Formed by the body. Therefore, the vibration energy generated from the spindle motor can be converted into heat energy. As a result, vibrations from the spindle motor to the magnetic disk or the magnetic head can be reduced or eliminated, and the occurrence of read / write errors can be prevented. In addition, since vibration from the spindle motor to the housing can be reduced or eliminated, the problem of noise due to the vibration of the housing itself can be solved.
Furthermore, since the viscoelastic body is formed of an acrylic adhesive, it has excellent heat resistance and vibration damping properties.

When the acrylic pressure-sensitive adhesive is crosslinked so that the gel fraction is 90% or more, the amount of gas generated is small and the contamination of the magnetic disk can be suppressed to a minimum. It is suitable as a damping material for hermetically sealed magnetic disk devices.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a magnetic disk device provided with a damping material of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a conventional magnetic disk device.

[Explanation of symbols]

 3 Spindle motor 6 Case 7 Damping material

Claims (2)

[Claims] 1. A damping material arranged between a spindle motor of a magnetic disk device and a housing for housing the spindle motor, wherein the damping material is a viscoelastic body made of an acrylic adhesive. Damping material characterized by being formed. 2. The gel pressure ratio of the acrylic pressure-sensitive adhesive is 90.
The vibration damping material according to claim 1, wherein the vibration damping material is crosslinked so as to have a content of at least%.