JP2005320475A - Polishing composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasive composition capable of uniformly abrading the surface of an object to be abraded without causing (or with hardly causing)scratch marks, particularly an abrasive composition without causing scratch marks on the surface of a magnetic disk substrate or capable of forming a uniform texture with extremely reduced scratch marks, if any. <P>SOLUTION: In the abrasive composition having an abrasive material and a dispersion medium for dispersing the abrasive material, fullerene is used as the abrasive material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention mainly relates to a polishing composition for texturing a surface (both sides or one side) of a magnetic disk substrate.

  A magnetic disk provided in a hard disk drive (HDD) is manufactured by forming a layer (magnetic layer) made of magnetic grains on the surface of a disk substrate made of aluminum or glass by sputtering rig or the like. In such a magnetic disk, in order to increase the recording density and the capacity, it is necessary to grow the magnetic grains smaller and uniformly on the disk substrate. For this reason, in magnetic disks using an aluminum disk substrate (aluminum substrate), the surface of the aluminum substrate is subjected to texture processing that gives fine streaks or scratches (textures) with an abrasive having higher hardness. However, recently, it has been demanded to apply a texture process to a disk substrate (glass substrate) made of glass having a hardness higher than that of aluminum.

  Such texturing is usually performed by supplying a polishing liquid containing an abrasive to an artificial leather tape, non-woven tape or polishing tape, and pressing the tape onto a magnetic disk substrate rotated at high speed for polishing. Is called. At that time, there is a problem that scratches easily enter the surface of the magnetic disk substrate. In particular, the glass substrate has a problem that it is difficult to make a uniform scratch as a texture because of its high hardness and brittleness.

  Further, conventionally, for example, diamond, CBN, aluminum oxide or the like has been used as a polishing material for texture processing. However, in the precision polishing processing accompanying the recent increase in capacity of HDD, There was also a problem that the polishing could not be performed uniformly and the generation of scratches could not be suppressed or prevented.

  Therefore, as means for uniformly and finely texturing the surface of a magnetic disk substrate, Patent Document 1 and Patent Document 2 propose a polishing composition using polycrystalline diamond particles as an abrasive. The former is a texture processing liquid for magnetic disk substrates, an aqueous solution containing about 1 to 25% by weight of a glycol compound as a surfactant, and polycrystalline diamond particles having an average particle diameter of 1 to 20 nm of 0.001 to 3% by weight. And aggregated polycrystalline diamond particles having an average particle diameter of 0.01 to 2 μm. The latter is a polishing slurry used for texturing the surface of a glass substrate, and disperses the aggregated polycrystalline diamond particles composed of polycrystalline diamond particles having an aggregated particle diameter of 0.5 μm or less, and the aggregated polycrystalline diamond particles. It is composed of water or a water-based aqueous solution.

  In addition, diamond particles (diamond abrasive grains) are used as an abrasive as described above, and are also fixed to a cutting edge portion of a dicing blade used for dicing of a semiconductor device. It has been proposed to use fullerene such as C60, which is considered to have a hardness higher than that of diamond in terms of molecular theory, as the abrasive grains provided at the blade tip portion (Patent Document 3).

JP 2002-30275 A JP 2002-370158 A JP-A-10-177975

  However, the polishing liquid described in the above-mentioned Patent Document 1 and Patent Document 2, that is, the polishing liquid using polycrystalline diamond as the polishing material is still sufficient in that the frequency of occurrence of scratches is relatively high. However, when texture processing is performed using this, there is a problem that scratches are generated, and thus the yield is lowered and the manufacturing cost of the hard disk is increased accordingly.

  In the above description, the problems in texturing the surface of the magnetic disk substrate using a conventional abrasive such as diamond particles have been described. However, such problems are caused by precision polishing of the surface of a magnetic head or the like. In this case, as long as a conventional abrasive is used, the same occurs.

  The present invention addresses the above-described problems, and can polish the surface of a magnetic disk substrate or a magnetic head with the required fine scratches, and at the same time prevent or suppress the occurrence of scratches, particularly a magnetic composition. An object of the present invention is to provide a polishing composition suitable for texturing the surface of a disk substrate.

  In order to achieve the above object, the present invention is characterized in that a polishing composition having an abrasive and a dispersion medium for dispersing the same contains fullerene as the abrasive.

  The abrasive in the present invention may substantially contain only fullerene, or may contain fullerene and diamond. Whether or not to include diamond in addition to fullerene is determined in consideration of the condition of the surface to be polished and the material cost.

  The polishing composition of the present invention preferably contains fullerene as an abrasive and water as a dispersion medium, and further contains a glycol solvent as a surfactant. It is preferable to use water as a dispersion medium because it has advantages such as low cost, easy availability, and no pollution of the environment, and it is preferable to use a surfactant because of this. This is because the dispersion stability of the polishing liquid) can be maintained. In addition, when water is used as the dispersion medium, it is preferable to use a glycol solvent that is compatible with water as the surfactant because the heat generated during the polishing process is cooled and the wettability to the object to be polished is reduced. This is because the polishing property is improved and the polishing property is improved. Furthermore, as the fullerene in this case, it is preferable to use what has been subjected to hydrophilic treatment in advance. This is because the dispersibility of fullerene in water as a dispersion medium can be further enhanced.

  The fullerene contained as an abrasive in the polishing composition of the present invention is considered to be higher in hardness than diamond in terms of molecular theory, and has a particle structure that hardly causes scratches on the surface to be polished during polishing. Is. Therefore, by using the polishing composition of the present invention containing such fullerene for texturing of a magnetic disk substrate, not only when the magnetic disk substrate is an aluminum substrate, but also when it is a harder glass substrate. In addition, a required uniform scratch (texture) can be made on the surface of the substrate, and processing without or with little scratch can be performed. In addition, by using a polishing composition containing fullerene as an abrasive as described above, the surface of a magnetic head or the like that requires precise polishing can be uniformly polished, and the surface can be finished with less scratches. .

  The present invention relates to a polishing composition (mainly polishing liquid) containing fullerene as an abrasive. In the polishing composition of the present invention, a known surfactant, dispersant, etc. may be added in order to maintain the dispersion stability. As the surfactant, a glycol solvent is preferably used. When water is used as the solvent, a glycol solvent compatible with water is preferably used, and ethylene glycol or propylene glycol is more preferably used. The primary particle size of fullerene as an abrasive contained in the polishing composition of the present invention is preferably 1 nm to 500 nm, more preferably 10 nm to 300 nm. The primary particle size in this range is preferable because if the particle size is less than 1 nm, the polishing efficiency is low because the polishing power is small, and if it exceeds 500 nm, scratches are likely to occur.

  Fullerene is an allotrope of carbon typified by diamond and graphite, and is a general term for spherical macromolecules in which carbon molecules are linked on the surface. Its molecular structure is a soccer ball type as typified by C60, but there are a plurality of types such as an elliptical shape and a bowl shape depending on the combination of carbon atoms. The diameter of the macromolecule is about 1 nm. In addition, fullerenes are considered to be harder than diamond in terms of molecular theory because they have a soccer ball-like crystal structure. A fine and high-hardness abrasive is required to make fine scratches on hard and brittle materials such as glass substrates. Since fullerene satisfies such requirements, by using it as an abrasive, it is possible to make fine scratches on the surface to be polished and finish the surface without scratches. Therefore, by polishing (texturing) the surface of the hard disk substrate using the polishing composition of the present invention containing such fullerene as an abrasive, the yield can be improved, and the manufacturing cost of the hard disk is correspondingly increased. Can be reduced.

  In Patent Document 3, a dicing blade comprising a rotating hub, a blade provided along the outer periphery of the rotating hub, and an abrasive provided on the blade, and fullerene particles used as the abrasive. Has been proposed. However, the dicing blade described in this patent document is used for cutting a silicon wafer or the like, and what is a polishing composition for polishing a surface of a magnetic disk substrate or the like as in the present invention to obtain a scratch-free surface. , Objects, objects to be used, actions and the like are different.

  The polishing composition of the present invention is mixed by adding an appropriate dispersion medium such as water or an organic solvent to the abrasive, and mixed with a media agitation disperser such as a sand mill or a ball mill, an ultrasonic disperser or a high speed agitation disperser. It can be produced by a dispersion treatment. Since the hardness of the abrasive is high, in order to prevent impurities from being mixed, it is preferable to carry out a dispersion treatment with an ultrasonic disperser or a high-speed stirring disperser. In addition to the dispersion medium, a surfactant, a dispersant, a preservative, an antifoaming agent, and the like may be added. Moreover, it is desirable to filter for the purpose of removing coarse particles after the dispersion treatment.

[Example]
Examples of the present invention will be described below together with comparative examples. In the following, “parts” means “parts by weight” unless otherwise specified.

・ Fullerene (MR6LP manufactured by Kishida Chemical Co., Ltd.) [Abrasive] 0.1 part ・ Water [dispersion medium] 49.9 parts ・ Ethylene glycol [surfactant] 50.0 parts

  The mixture having the above composition was dispersed with a high-speed agitation type disperser, and then dispersed for 1 hour with an ultrasonic disperser. Subsequently, the obtained processed product (mixture) was taken out and filtered through a filter (pore size: 1 μm). The polishing composition (polishing liquid) thus obtained was used as a test sample of Example 1.

  A test sample of Example 2 was prepared in the same manner as in Example 1 except that the abrasive was changed to 0.05 part of fullerene and 0.05 part of polycrystalline diamond (Sumitomo Coal Mining).

  A test sample of Example 3 was prepared in the same manner as in Example 1 except that the abrasive was changed to 0.05 part of fullerene and 0.05 part of alumina.

[Comparative Example 1]
A test sample of Comparative Example 1 was produced in the same manner as Example 1 except that the abrasive was changed to 0.1 part of polycrystalline diamond.

<< Evaluation test and evaluation results >>
In order to examine the polishing performance of each of the test samples obtained in the above examples and comparative examples, the surface of a glass magnetic disk substrate (hereinafter, also simply referred to as “magnetic disk” or “disk”) is used to texture the test samples. processed. FIG. 1 schematically shows the texture processing. As shown in FIG. 1, a polishing composition (test sample) 1 is supplied from a nozzle 2 to the surface of a rotating magnetic disk 5, and a tape-like nonwoven fabric 3 running in a direction opposite to the rotating direction is a rubber roller. 4 is pressed against the surface of the magnetic disk 5. Then, the surface of the magnetic disk 5 is polished, that is, textured, by the polishing composition that has entered between the nonwoven fabric 3 and the magnetic disk 5. For this texturing, a disk polishing machine made by Maxell was used, and the polishing conditions were as shown in Table 1.

  The textured disc was evaluated as follows. The textured magnetic disk was observed with a surface observation device MicroMAX (VMX-2100 manufactured by Vision Cytec Co., Ltd.). As an evaluation of scratch properties, the case where there is a scratch on the surface of the disk is regarded as a defective product, the case where there is no scratch on the disk is regarded as a non-defective product, and the ratio of the number of non-scratch scratched disks in 100 processed disks, that is, did. Table 2 shows the evaluation results.

  As can be seen from Table 2, in the samples of Examples 1, 2, and 3, the frequency of occurrence of scratches on the disk surface is low, and the yield is 94% or more. On the other hand, in the sample of Comparative Example 1, not only small scratches like a comet but also deep scratches occurred on the disk surface, and the yield was low.

It is a figure which shows typically the mode of the texture process performed in order to investigate the performance of the polishing composition obtained by the Example and comparative example of this invention.

Explanation of symbols

1 Polishing composition
2 nozzles
3 Nonwoven fabric
4 Rubber roller
5 Magnetic disk

Claims (5)

  A polishing composition comprising an abrasive and a dispersion medium for dispersing the abrasive, the polishing composition comprising fullerene as the abrasive.   The polishing composition according to claim 1, comprising fullerene and diamond as the abrasive.   2. The polishing composition according to claim 1, comprising only fullerene as an abrasive.   2. The polishing composition according to claim 1, comprising fullerene as an abrasive and water as a dispersion medium, and further comprising a glycol solvent as a surfactant.   The polishing composition according to claim 4, wherein the fullerene is previously hydrophilically treated.

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