JPH10214464A - Production of vibration damping material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to produce a vibration damping material consisting of a single sheetlike molding having a desired thickness with good productivity with the extremely little amt. of the gases to be generated. SOLUTION: Acrylic rubber (Mooney viscosity 40, white) is subjected to mastication by a mixing roll without raising its heat and thereafter, the rubber is extruded by an extruder of a screw temp. of 150 deg.C, a cylinder temp. of 170 deg.C and a head temp. of 170 deg.C at an extrusion rate of 0.5m/min to obtain the molded sheet. The thickness and surface state of the molded sheet are adjusted by a roller head of 150 deg.C arranged right behind the head. The molded sheet is thereafter irradiated with 50kGy electron beans and is then subjected to cross linking, then drying (degassing) to obtain the sheet having 4mm thickness. The sheet obtd. in such a manner has the amt. of the gases to be generated as extremely small as <40ppm. The sheet having the extremely outstanding characteristics as the vibration damping material, for example, 1.5 to 2.3kg/cm<2> in the stress at the time of 20% compression is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a damping material used for damping a voice coil motor (VCM) for moving an actuator arm of a magnetic disk drive.

[0002]

2. Description of the Related Art The actuator arm of a magnetic disk drive is moved by a voice coil motor (VCM). When the VCM vibrates and the actuator arm vibrates, the read head vibrates in conjunction therewith, causing a read error or worst case. In this case, the head and the magnetic disk come into contact with each other, which may cause the magnetic disk to be destroyed. Therefore, in order to eliminate the above-mentioned problems, a vibration damper made of a viscoelastic body is sandwiched between a VCM (usually formed as a unit) and the inside of a housing for housing the VCM. A material is provided to suppress the vibration of the VCM. Since such a vibration damping material is used by being sandwiched between the inside of the housing and the upper portion of the VCM, the thickness is usually about 0. 0 depending on the type of the magnetic disk device and the disk size.
It is about 5 to 7 mm.

[0003]

Conventionally, an adhesive or a foam has been used as a damping material made of a viscoelastic material. However, the pressure-sensitive adhesive is usually in the form of a sheet having a thickness of 0.2 mm or less due to its manufacturing method.
m, and the laminating operation is complicated and productivity is poor. In addition, since a plurality of layers are bonded, there is a disadvantage that the accuracy of thickness is lacking. In addition, the foaming agent used as a production raw material remains in the foam,
Foaming gas resulting from this is generated in the magnetic disk drive. Magnetic disks are easily corroded by corrosive gases,
Also, since the inside of the magnetic disk drive is in a sealed state,
Even the generation of a small amount of gas may contaminate the magnetic disk or damage the magnetic disk.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has produced a vibration-damping material made of a single sheet-like molded body having a very small amount of generated gas and a predetermined thickness. An object of the present invention is to provide a method of manufacturing a vibration damping material that can be manufactured with good performance.

[0005]

According to one aspect of the present invention, there is provided a method of manufacturing a vibration damping material for a voice coil motor (VCM) of a magnetic disk, comprising the steps of: Alternatively, a kneaded product obtained by kneading an additive for improving at least one of the moldability of the elastomer and the damping property of the damping material is extruded by an extruder into an elastomer, and formed into a sheet having a predetermined thickness. In addition, the present invention is characterized in that a vibration damping material is produced by using the sheet-shaped molded body for a viscoelastic body portion of the vibration damping material. With such a configuration,
Since the elastomer or the kneaded product obtained by kneading the additive with the elastomer is extruded into a sheet, the sheet thickness can be adjusted with high precision. In addition, a sheet can be continuously obtained, and a plurality of sheet pieces serving as viscoelastic material portions of the vibration damping material can be obtained at a time by punching from a large area sheet, so that the vibration damping material can be manufactured with high productivity. Further, since the sheet does not contain a foaming material, the amount of gas generated when the viscoelastic body portion of the vibration damping material is used can be extremely reduced.

In the method for producing a vibration-damping material of the present invention, the additive for improving the vibration-damping property of the vibration-damping material is a cross-linking agent.
It is preferable to use from 8 to 8 parts by weight. With such a configuration, the sheet-shaped molded article has an appropriate degree of crosslinking, and it is easy to obtain a preferable compressive stress as a viscoelastic body portion of the vibration damping material.

In the method for producing a vibration damping material according to the present invention, radiation is applied to the sheet-like molded body at 30 to 150 kGy.
It is preferable to cross-link the sheet-like molded product by irradiation, and to use the cross-linked sheet-like molded product for the viscoelastic body portion. With such a configuration, it is possible to obtain a preferable compressive stress as the viscoelastic body portion of the vibration damping material. It will be easier.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Elastomers used in the present invention include acrylic rubber, NBR (acrylonitrile-butadiene copolymer rubber), SBR (styrene-butadiene copolymer rubber), isoprene rubber, butyl rubber, fluororubber and the like. Can be mentioned. In use, it is desirable to select and use a substance having a high purity and a small content of a gas generating substance. Even if the silicone rubber generates little gas, it cannot be used because only a small amount of silicone gas adheres to the disk and causes the disk to break. In the present invention, the elastomer is formed into a sheet by an extruder. By using such an extruder, continuous production is possible and the thickness of the sheet can be adjusted with high precision. The elastomer formed into a sheet by the extruder is dried (degassed) as necessary, and a double-sided adhesive tape is attached to at least one main surface, and punched into a predetermined shape to obtain a product (vibration damping material). That is, the sheeted elastomer becomes the viscoelastic body of the vibration damping material.

Although the form of the extruder is not particularly limited, a single-screw or twin-screw extruder is usually used. The die attached to the extruder is preferably a fishtail die. This is when extruding a highly elastic elastomer,
If the pressure applied to the elastomer by the compression by the screw is not sufficiently released in the die, the deformation of the sheet will be significant due to the residual stress remaining in the elastomer immediately after the elastomer comes out from the die and even after being molded into a sheet. However, if a fishtail die is used, the pressure applied to the elastomer in the die can be sufficiently released, and the above-mentioned problem can be solved.

The extrusion temperature is appropriately adjusted according to the type of the elastomer, but is usually set in the range of 80 to 180 ° C. If the temperature is higher than 180 ° C., the elastomer may be thermally cross-linked to cause surface roughening, or it may not be possible to form a sheet. This is because there is a possibility that deformation or surface roughness may occur.

When the deformation and surface roughness become severe, the adhesion of the damping material to the inner surface of the housing or the VCM is reduced, and it becomes difficult to obtain a sufficient damping action. Therefore, a roller head may be provided immediately after the die, and the roller head may be used to correct the surface roughness of the sheet obtained by extrusion or to reduce the residual stress.

The extrusion speed is usually from 0.1 m / min to 1 m / min. This means that, when it is greater than 1 m / min, the flow of elastomer in the extruder is extruded at the extrusion speed (screw).
This is because it becomes difficult to follow the propulsion force, and the surface tends to be rough, and if it is slower than 0.1 m / min, the productivity tends to decrease.

In the present invention, various additives can be blended with the elastomer to be extruded in order to improve the extrusion moldability of the elastomer or the vibration damping material (viscoelastic body portion). For example, additives mainly improving the extrusion moldability of the elastomer include a tackifier, a plasticizer, and a filler. Elastomers generally have high elasticity and cannot be said to be easy to be formed into a sheet by extrusion.However, when the tackifier, plasticizer, filler, etc. are added, the elasticity is reduced and extrusion is performed. It becomes easy to make a sheet. On the other hand, additives that mainly improve the damping properties of damping materials include:
Vulcanizing agents, vulcanization accelerators, crosslinking agents, ultraviolet absorbers, antioxidants and the like can be mentioned. In particular, when a vulcanizing agent, a vulcanization accelerator, and a cross-linking agent are used, a cross-linked structure can be more positively introduced into a molded article, and the compression stress characteristics of the molded article can be improved. It should be noted that since these low molecular weight additives tend to cause gas generation, it is necessary to select and use ones that hardly cause gas generation when used.

These low molecular weight additives are kneaded with the elastomer by a mixing roll or the like before the extrusion of the elastomer. In the case where a crosslinking agent is used, if the crosslinking reaction is not completed by the extrusion operation, the sheet obtained after the extrusion operation is subjected to a heat treatment to terminate the crosslinking reaction.

Further, the extruded sheet-like molded product of the elastomer may be irradiated with radiation such as an electron beam or γ-ray to perform crosslinking. In this case, the irradiation dose of radiation is usually 30 to 15
0 kGy, preferably 50-100 kGy.

When the low molecular weight additive is not added to the elastomer, the elastomer may be masticated as required.

In the present invention, the type of elastomer used, the type and amount of additives, the degree of cross-linking, etc. are appropriately adjusted under the above-mentioned preferable extrusion conditions to obtain a sheet-like molded product finally obtained. Stress at the time of 20% compression is 0.8 to 5 kg / cm ² , preferably 1 to 3 kg / cm
^It is better to manufacture so as to be within the range of ² . By providing such a compressive stress, the sheet-shaped formed body (vibration damping material) can be sufficiently applied to the voice coil motor or the housing without the housing made of the aluminum processed product usually being closed or deformed. Because of the close contact, an excellent vibration damping action can be obtained. It should be noted that the above-described compressive stress cannot be obtained with a conventional vibration damping material formed by laminating a plurality of adhesive materials or a foam damping material.

[0018]

The present invention will be described in more detail with reference to the following examples. (Example 1) Acrylic rubber (AR-31, manufactured by Nippon Zeon Co., Ltd., Mooney viscosity 40, white) was masticated with a mixing roll without applying temperature, and extruded with an extruder according to the conditions shown in Table 1. Extrusion was performed at a speed of 0.5 m / min. A roller head was disposed immediately after the head, and the thickness and surface condition of the formed sheet were adjusted. Next, the molded sheet was irradiated with an electron beam at 50 kGy, crosslinked, and dried (degassed) to obtain a sheet having a thickness of 4 mm.

Example 2 Acrylic rubber (AR-31,
The mixture was extruded at a rate of 0.2 m / min using an extruder according to the conditions shown in Table 1 under the conditions shown in Table 1 by mixing with a mixing roll without applying a temperature. Adjustment of the thickness of the molded sheet was performed at the gap of the base of the head. Next, the molded sheet was irradiated with an electron beam at 50 kGy, crosslinked, and dried (degassed) to obtain a sheet having a thickness of 4 mm.

Example 3 Acrylic rubber (AR-31,
A cross-linking agent (Diak No. 1, manufactured by Dupont) was blended with ZEON Co., Ltd., Mooney viscosity 40, white according to the conditions shown in Table 1, and the mixture was kneaded with a mixing roll without applying temperature. The obtained kneaded product was extruded at an extrusion speed of 0.5 m / min with an extruder according to the conditions shown in Table 1. A roller head was disposed immediately after the head, and the thickness and surface condition of the formed sheet were adjusted. After that, 150 minutes by heating furnace
The mixture was heated at 10 ° C. for 10 minutes to terminate the cross-linking reaction of the molded sheet to obtain a sheet having a thickness of 4 mm.

Example 4 A sheet having a thickness of 4 mm was obtained in the same manner as in Example 1 except that the extrusion speed was changed to 2 m / min.

Example 5 A sheet having a thickness of 4 mm was obtained in the same manner as in Example 1 except that the temperature of the extruder and the temperature of the roller head were changed as shown in Table 1.

(Example 6) The procedure of Example 1 was repeated except that the temperature of the extruder was changed as shown in Table 1.
A thick sheet was obtained.

Comparative Example 1 90 parts by weight of 2-ethylhexyl acrylate monomer and 10 parts by weight of acrylic acid monomer were mixed, and 1 part by weight of azobisisobutyronitrile was added as a polymerization initiator. The polymerization was carried out. A product obtained by adding 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane as a crosslinking agent to the obtained polymer is coated on a polyester separator and heated at 130 ° C. for 3 minutes to give a thickness of 0. A 1 mm-thick baseless adhesive sheet was obtained. Next, this adhesive sheet was laminated with a laminator for 40 layers to a thickness of 4 mm.

Comparative Example 2 A sheet-like polyethylene foam having a thickness of 4 mm was prepared.

The amount of gas generated in the sheet obtained above and 20%
The stress during compression was investigated. Further, the surface state and color tone of the sheet of the example were visually observed. The amount of gas generated from the sheet and the stress at the time of 20% compression were measured by the following methods.

[Amount of generated gas] About 1.5 g of a sample
At 24 ° C. for 24 hours and a headspace sampler (H
In S), the generated gas was sent to a gas chroma-mass spectrum (GC-MS) and analyzed and quantified. HS is H
P7694 (manufactured by Hewlett-Packard), GC-M
S is HP5890A seriesII plus / H
P5972 (manufactured by Hewlett-Packard) was used.

[Stress at 20% Compression] First, a sample was cut into a size of 15 mm × 15 mm, a compression test jig was attached to a universal tensile tester, and the sample was set on the compression test jig. The sample is compressed at a speed of 5 mm / min until the thickness of the sample becomes 20%, and the stress at that time is measured. The measurement is performed at 25 ° C. × 60% RH.

Table 1 shows the evaluation results of the sheets of the examples.
It was shown to.

[Table 1] As shown in Table 1, each of the sheets of Examples 1 to 6 had an amount of generated gas of less than 40 ppm and an extremely small amount of generated gas. On the other hand, the amount of generated gas of the sheet of Comparative Example 1 was 65 ppm, and the amount of generated gas of the sheet of Comparative Example 2 was 316 ppm.

The stresses of the sheets of Examples 1 to 6 at the time of 20% compression were 1.9, 1.8, 2.1,.
At 5, 1.6, and 2.3 kg / cm ^2, it had excellent compressive stress characteristics. In contrast, the stress of the sheet of Comparative Example 1 at 20% compression was 0.76 kg / cm ^2, which was small, and the stress of the sheet of Comparative Example 2 at 20% compression was 0.32.
kg / cm ^2, which was extremely small, and none of them could provide a good vibration damping action.

The sheets of Examples 1 to 3 all had good surface conditions, had a white color tone, and did not show any thermal deterioration. The surface conditions of the sheets of Examples 4 to 6 were at an acceptable level although the surface was slightly rough.

[0032]

As described above, according to the method for producing a vibration damping material of the present invention, a sheet having a predetermined thickness is extruded by extruding an elastomer or a kneaded product obtained by kneading an additive with an elastomer as required. By forming this sheet-shaped molded body into a viscoelastic body part of the vibration-damping material to form a vibration-damping material, the amount of generated gas is extremely small, and excellent vibration-damping characteristics are provided. A vibration damping material having a desired thickness can be manufactured with high productivity.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Matsuoka 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Tokio Fujita 1-1-2 Shimohozumi, Ibaraki-shi, Osaka No. Nitto Denko Corporation (72) Inventor Keisaku Okada 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (3)

[Claims] 1. A method of manufacturing a vibration damping material for a voice coil motor of a magnetic disk, the method comprising: improving at least one of an elastomer or an elastomer in the elastomer and a vibration damping property of the vibration damping material. The kneaded product obtained by kneading the additives is extruded by an extruder, formed into a sheet having a predetermined thickness, and the sheet-shaped molded body is used as a viscoelastic body portion of the vibration damping material to produce a vibration damping material. Characteristic method of manufacturing damping material. 2. The method for producing a vibration damping material according to claim 1, wherein the additive for improving the vibration damping property of the vibration damping material is a crosslinking agent, and the crosslinking agent is used in an amount of 1 to 8 parts by weight per 100 parts by weight of the elastomer. Method. 3. A sheet-like molded product is irradiated with radiation for 30 to 150 days.
The method for producing a vibration damping material according to claim 1, wherein the sheet-like molded body is cross-linked by irradiation with kGy, and the cross-linked sheet-shaped molded body is used for a viscoelastic body portion.