JP2010029981A - Abrasive cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasive cloth that ensures less scratch damage compared with a conventional abrasive cloth, while decreasing surface roughness of a substrate. <P>SOLUTION: The abrasive cloth has a nonwoven cloth formed by interweaving bundles of extra-fine fibers with an average fiber diameter of 0.3-3.0 μm, and in a cross section of the abrasive cloth that intersects a thickness direction thereof, there are 50-1,000 cross-sectioned bundles of the extra-fine fibers/mm<SP>2</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an abrasive cloth, and more particularly, to an abrasive cloth that can be suitably used when an aluminum alloy substrate or a glass substrate used for a magnetic recording disk is polished and / or cleaned with an ultra-high precision finish.

  Magnetic recording disks are required to be smoothed to the limit of the disk surface as the capacity and storage density are increased. Specifically, it is required to reduce the substrate surface roughness to 0.2 nm or less and minimize scratches on the substrate surface called scratch defects.

  Slurry grinding is performed on the magnetic recording disk substrate with a polishing pad made of hard polyurethane foam, etc., and then free abrasive grains are adhered to the surface of the polishing cloth in order to increase the smoothness by grinding minute scratches and protrusions. Polishing is performed.

  Specifically, the polishing process is performed by continuously reciprocating in the radial direction of the substrate while pressing the tape-like polishing cloth (polishing tape) against the substrate with a rubber roller while the substrate of the magnetic recording disk is continuously rotated. Run the abrasive tape. At this time, the slurry is supplied between the polishing tape and the substrate, and the free abrasive grains contained in the slurry are gripped in a state of being finely dispersed in the fibers on the surface of the polishing tape and pressed against the substrate for polishing. Yes.

  As an abrasive cloth, for example, in Patent Documents 1 to 4, the fibers constituting the nonwoven fabric are made ultrafine to reduce the substrate surface roughness of the magnetic recording disk, and the nonwoven fabric is impregnated with an elastic polymer to provide cushioning properties. Thus, the disclosure of minimizing scratch defects has been made, and certain results have been achieved.

  In recent years, a technique has also been disclosed in which ultrafine fibers (nanofibers) are dispersed on the surface of a polishing cloth (Patent Document 5).

However, there is a demand for further suppressing scratch defects due to recent improvements in the accuracy of polishing.
Japanese Patent Laid-Open No. 2001-1252 JP 2002-273650 A JP-A-6-272114 Japanese Patent No. 3457478 JP 2007-144614 A

  An object of the present invention is to provide a polishing cloth that can suppress scratch defects more than a conventional polishing cloth while achieving a reduction in substrate surface roughness.

That is, the present invention comprises a nonwoven fabric in which bundles of ultrafine fibers having an average fiber diameter of 0.3 to 3.0 μm are entangled, and in a cross section orthogonal to the thickness direction of the polishing cloth, the cross section of the ultrafine fiber bundles Is a polishing cloth characterized by the presence of 50 to 1000 pieces / mm ² .

  According to the present invention, the presence of a large number of fibers oriented in the thickness direction in the polishing cloth sheet on the polishing surface makes the gripping ability of the abrasive grains moderately weak compared to conventional polishing cloths, and there are defects such as scratches. It is possible to smooth the substrate surface without generating.

  The polishing cloth of the present invention comprises a nonwoven fabric formed by entanglement of a bundle of ultrafine fibers (ultrafine fiber bundle). By adopting ultrafine fibers, the surface roughness of the object to be polished can be reduced.

  Examples of the polymer forming the ultrafine fiber include polyester, polyamide, polyolefin, polyphenylene sulfide (PPS), and the like. Many polycondensation polymers represented by polyesters and polyamides have a high melting point, and are more preferable because of excellent heat resistance against heat generated during polishing. Specific examples of the polyester include polyethylene terephthalate, polybutylene terephthalate, and potytrimethylene terephthalate. Specific examples of the polyamide include nylon 6, nylon 66, nylon 12, and the like.

  In addition, the polymer constituting the ultrafine fiber may be copolymerized with other components, and may contain additives such as particles, flame retardant, and antistatic agent.

  It is important that the average fiber diameter of the ultrafine fibers is 0.3 to 3.0 μm. By setting the thickness to 3.0 μm or less, preferably 2.5 μm or less, the surface roughness of the object to be polished can be reduced. On the other hand, when the thickness is 0.3 μm or more, preferably 0.5 μm or more, fiber strength and rigidity can be maintained, so that polishing can be performed efficiently.

  As will be described later in the measurement methods of the examples, when fibers having a fiber diameter exceeding 10 μm are mixed, the fibers are excluded from the measurement target of the average fiber diameter as not corresponding to the ultrafine fibers. And

  As a form of the ultrafine fiber bundle, the ultrafine fibers may be slightly separated from each other, may be partially bonded, or may be aggregated.

  In the nonwoven fabric used for the polishing cloth of the present invention, fibers thicker than the ultrafine fibers defined above may be mixed. By doing so, the strength of the polishing cloth can be reinforced and the cushioning property can be improved. As the polymer that forms fibers thicker than the ultrafine fibers, the same polymers as those constituting the ultrafine fibers described above can be employed. The blending amount of the fibers thicker than the ultrafine fibers with respect to the nonwoven fabric is 30% by mass or less, more preferably 10% by mass or less, so that the smoothness of the polishing cloth surface can be maintained.

  Nonwoven fabrics used in the polishing cloth of the present invention include short fiber nonwoven fabrics obtained by forming needle webs and water jet punches after forming staple webs using cards and cross wrappers, spunbond methods, and melt blown methods. It is possible to employ a long-fiber non-woven fabric obtained by a method, a non-woven fabric obtained by a papermaking method, or the like. Among these, the short fiber nonwoven fabric and the spunbond nonwoven fabric are preferable because the embodiment of the ultrafine fiber bundle as described later can be obtained by the needle punching process.

  In the polishing cloth of the present invention, it is also preferable that the non-woven fabric contains an elastic polymer. Due to the binder effect of the elastic polymer, it is possible to prevent the ultrafine fibers from falling off the polishing cloth, and to impart cushioning properties to the polishing cloth, thereby reducing scratch defects.

  Examples of the elastic polymer include polyurethane, polyurea, polyurethane / polyurea elastomer, polyacrylic acid, acrylonitrile / butadiene elastomer, and styrene / butadiene elastomer.

  Among these, polyurethane elastomers such as polyurethane and polyurethane / polyurea elastomer are preferable. As the polyol component of the polyurethane-based elastomer, polyester-based, polyether-based, polycarbonate-based diols, or copolymers thereof can be used. Moreover, as a diisocyanate component, aromatic diisocyanate, alicyclic isocyanate, aliphatic isocyanate, etc. can be used.

  The weight average molecular weight of the polyurethane elastomer is preferably 50,000 to 300,000. By setting the weight average molecular weight to 50,000 or more, more preferably 100,000 or more, and further preferably 150,000 or more, it is possible to maintain the strength of the polishing cloth and prevent the fine fibers from falling off. In addition, by setting the viscosity to 300,000 or less, more preferably 250,000 or less, it is possible to suppress the increase in the viscosity of the polyurethane solution and facilitate the impregnation of the ultrafine fiber layer.

  The elastic polymer may contain an elastomer resin such as polyester, polyamide, or polyolefin, an acrylic resin, an ethylene-vinyl acetate resin, or the like.

  In addition, additives such as colorants, antioxidants, antistatic agents, dispersants, softeners, coagulation modifiers, flame retardants, antibacterial agents, and deodorants are blended in the elastic polymer as necessary. Also good.

  As a content rate of an elastic polymer, 5-200 mass% is preferable with respect to the nonwoven fabric formed by a very fine fiber bundle being entangled. The surface state, cushioning properties, hardness, strength, etc. of the polishing cloth can be adjusted by the content. By setting the content to 5% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more, fiber dropout can be reduced. On the other hand, by making it 200% by mass or less, more preferably 100% by mass or less, and further preferably 80% by mass or less, workability and productivity are improved, and a state in which ultrafine fibers are uniformly dispersed on the surface is obtained. Can do.

The basis weight of the portion of the polishing cloth of the present invention excluding the reinforcing layer described later is preferably 100 to 600 g / m ² . By making it 100 g / m ² or more, more preferably 150 g / m ² or more, it is excellent in form stability and dimensional stability of the polishing cloth, and suppresses processing unevenness and scratch defects due to elongation of the polishing cloth during polishing processing. be able to. On the other hand, by making it 600 g / m ² or less, more preferably 300 g / m ² or less, the handling property of the polishing tape becomes easy, and the cushioning property of the polishing cloth is moderately suppressed. The pressure applied by the rubber roller can be appropriately propagated to the polishing surface to perform efficient polishing.

  Moreover, as thickness of the part except the reinforcement layer mentioned later of the polishing cloth of this invention, 0.1-10 mm is preferable. By setting the thickness to 0.1 mm or more, preferably 0.3 mm or more, the shape and dimensional stability of the polishing cloth are excellent, and processing unevenness due to elongation of the polishing cloth during polishing processing and generation of scratch defects can be suppressed. . On the other hand, when the thickness is 10 mm or less, more preferably 5 mm or less, the pressing pressure during polishing can be sufficiently propagated.

  Moreover, it is also preferable that the polishing cloth of the present invention has a reinforcing layer on the other surface (the surface on the side subjected to polishing) having the cut end of the ultrafine fiber bundle described later. By doing so, it is excellent in the form stability and dimensional stability of the polishing cloth, and it is possible to suppress the occurrence of processing unevenness and scratch defects due to the elongation of the polishing cloth during polishing. As the reinforcing layer, a woven fabric, a knitted fabric, a nonwoven fabric (including paper), a film-like material (plastic film, metal thin film sheet, etc.) and the like can be employed.

In the polishing cloth of the present invention, it is important that 50 to 1000 fiber bundles / mm ² exist in a cross section perpendicular to the thickness direction of the polishing cloth. In a general artificial leather type polishing cloth, the fine fibers are arranged almost perpendicular to the thickness direction (the surface is covered with the fine fibers lying on the surface), so the abrasive cloth is pushed against the rotating disk. At the time of the polishing process, the fine fibers lying on the surface grip the abrasive grains. As a result, the gripping ability of the abrasive grains becomes higher than necessary, there is no escape place for the abrasive grains, and scratches are likely to occur. On the other hand, the polishing cloth of the present invention has a brush-like structure because there are enough fibers arranged in the thickness direction on the polishing surface, and the pressing pressure of the abrasive grains during polishing is moderate as compared to conventional polishing cloths. As a result, it is possible to sufficiently suppress defects such as scratches. By setting it to 50 pieces / mm ² or more, preferably 100 pieces / mm ² or more, more preferably 200 pieces / mm ² or more, an effect of sufficiently suppressing defects such as scratches can be obtained. On the other hand, the strength of the polishing pad can be maintained by setting it to 1000 pieces / mm ² or less, more preferably 800 pieces / mm ² or less, and even more preferably 600 pieces / mm ² or less.

In the polishing cloth of the present invention, it is preferable that 10 to 150 pieces / mm ² of cut ends of the ultrafine fiber bundles on at least one surface, that is, the surface on the side subjected to polishing are present. By setting the cutting end of the ultrafine fiber bundle to 10 pieces / mm ² or more, more preferably 50 pieces / mm ² or more, the above brush-like structure can be more effectively taken. On the other hand, the strength of the polishing pad can be maintained by setting it to 150 pieces / mm ² or less, preferably 130 pieces / mm ² or less.

  In addition, the polishing cloth of the present invention preferably has 80 to 500 ultrafine fiber bundles per 1 cm width in a cross section parallel to the thickness direction of the polishing cloth. By setting the number to 80 or more per 1 cm width, more preferably 90 or more, and even more preferably 100 or more, the above brush-like structure can be more effectively taken. On the other hand, the strength of the polishing pad can be maintained by setting it to 500 or less, more preferably 300 or less, and even more preferably 200 or less.

  In the polishing cloth of the present invention, it is preferable that the surface of the surface to be subjected to polishing is subjected to napping treatment. By doing so, the above brush-like structure can be taken more effectively. Moreover, since it is excellent also in cushioning properties, scratch defects can be reduced. Next, a method for producing the polishing cloth of the present invention will be described.

  As a means for obtaining a nonwoven fabric in which ultrafine fiber bundles are entangled, it is preferable to use ultrafine fiber generating fibers. Although it is difficult to produce a nonwoven fabric directly from ultrafine fibers, by producing a nonwoven fabric from ultrafine fiber-generating fibers and generating ultrafine fibers from sea-island composite fibers in this nonwoven fabric, the ultrafine fiber bundles are intertwined Can be obtained.

  As ultra-fine fiber-generating fibers, two-component thermoplastic resins with different solvent solubility are used as sea components and island components, and the sea components are dissolved and removed using a solvent, etc., so that the island components are made into ultra-fine fibers. Alternatively, a two-component thermoplastic resin may be alternately disposed in a radial or multilayer manner on the fiber cross section, and a peelable composite fiber that is split into ultrafine fibers by separating and separating each component may be employed.

  Sea-island type fibers include sea-island type composite fibers that use a sea-island type composite base to spun two sea and island components together, and mixed spinning fibers that mix and spin the two sea and island components. However, sea-island type composite fibers are more preferable because ultrafine fibers having a uniform fineness can be obtained, and a sufficiently long ultrafine fiber can be obtained and contribute to the strength of the sheet-like material.

  As the sea component of the sea-island fiber, polyethylene, polypropylene, polystyrene, copolymerized polyester obtained by copolymerizing sodium sulfoisophthalic acid or polyethylene glycol, polylactic acid, or the like can be used.

  The dissolution removal of the sea component may be performed at any timing before, after applying, and after raising the elastic polymer.

  As a method for obtaining a nonwoven fabric, a method of entanglement of a web with a needle punch or a water jet punch as described above, a spunbond method, a melt blow method, a papermaking method, etc. can be adopted. In forming the bundle, it is preferable to perform processing such as needle punching or water jet punching.

  In the needle punching process, the number of barbs is preferably 1-9. By using one or more fibers, efficient fiber entanglement becomes possible. On the other hand, fiber damage can be suppressed by setting it to 9 or less.

  The total depth of the barb is preferably 0.05 to 0.09 mm. By setting the thickness to 0.05 mm or more, a sufficient catch on the fiber bundle can be obtained, so that efficient fiber entanglement becomes possible. On the other hand, it becomes possible to suppress fiber damage by setting it as 0.09 mm or less.

As a punching number, 4500-14000 piece / cm < ² > is preferable. By setting it to 4500 lines / cm ² or more, denseness can be obtained and high-precision finishing can be obtained. On the other hand, by setting it to 14000 pieces / cm < ² > or less, workability deterioration, fiber damage, and strength reduction can be prevented.

  Moreover, when performing a water jet punch process, it is preferable to perform water in the state of a columnar flow. Specifically, water may be ejected from a nozzle having a diameter of 0.05 to 1.0 mm at a pressure of 1 to 60 MPa.

The apparent density of the ultrafine fiber generating fiber nonwoven fabric after needle punching or water jet punching is preferably 0.15 to 0.30 g / cm ³ . By setting it to 0.15 g / cm ³ or more, the shape stability and dimensional stability of the polishing cloth are excellent, and the occurrence of processing unevenness and scratch defects due to the elongation of the polishing cloth during polishing processing can be suppressed. On the other hand, by setting it to 0.30 g / cm ³ or less, a sufficient space for applying the elastic polymer can be maintained.

  From the viewpoint of densification, the ultrafine fiber generating fiber nonwoven fabric obtained in this way is preferably shrunk by dry heat or wet heat, or both, and further densified.

  Solvents that dissolve easily soluble polymers (sea components) from ultrafine fiber-generating fibers include polyolefins such as polyethylene and polystyrene, organic solvents such as toluene and trichloroethylene, and sodium hydroxide for polylactic acid and copolymerized polyesters. An alkaline aqueous solution such as can be used. The ultrafine fiber generation processing (sea removal treatment) can be carried out by immersing the ultrafine fiber generation type fiber (nonwoven fabric made of) in a solvent and squeezing it.

  For the ultrafine fiber generation processing, known devices such as a continuous dyeing machine, a vibro-washer type sea removal machine, a liquid flow dyeing machine, a Wins dyeing machine, a jigger dyeing machine, and the like can be used.

  The ultrafine fiber generation processing may be performed before the napping treatment or after the napping treatment.

  The elastic polymer may be applied before or after the ultrafine fiber generation processing.

  As the solvent used for imparting the elastic polymer, N, N′-dimethylformamide, dimethyl sulfoxide and the like can be preferably used. Alternatively, an aqueous polyurethane dispersed as an emulsion in water may be used.

  The elastic polymer is applied to the non-woven fabric by immersing the non-woven fabric in an elastic polymer solution dissolved in a solvent, and then dried to substantially solidify and solidify the elastic polymer. In drying, you may heat at the temperature which does not impair the performance of a nonwoven fabric and an elastic polymer.

  The napping treatment of the polishing cloth can be performed using sandpaper or a roll sander. In particular, by using sandpaper, uniform and dense napping can be formed. Furthermore, in order to form uniform napping on the surface of the polishing pad, it is preferable to reduce the grinding load. In order to reduce the grinding load, for example, it is more preferable that the number of buff stages is multistage buffing with three or more stages, and the number of sandpaper used in each stage is in the range of 150 to 600 of JIS regulations.

  The polishing cloth of the present invention is preferably used as a polishing tape by cutting it into a tape having a width of 30 to 50 mm from the viewpoint of processing efficiency and stability.

  As a polishing method, it is preferable to polish a magnetic recording disk substrate made of an aluminum alloy or the like using the above-described polishing tape and slurry containing loose abrasive grains. As the slurry, those obtained by dispersing high-hardness abrasive grains such as diamond fine particles in an aqueous dispersion medium are preferably used. As an abrasive particle diameter, 0.2 micrometer or less is preferable from a viewpoint of the retainability and the dispersibility of the abrasive grain suitable for the ultrafine fiber which comprises the polishing cloth of this invention.

[Measuring method and processing method for evaluation]
(1) Melting point
Using a Perkin Elmaer DSC-7, the peak top temperature indicating the melting of the polymer at 2nd run was taken as the melting point of the polymer. At this time, the rate of temperature increase was 16 ° C./min, and the sample amount was 10 mg.

(2) Melt flow rate (MFR)
Sample pellets 4 to 5 g are put in a cylinder of an MFR electric furnace, and are loaded for 10 minutes from an orifice having a vertical hole with an outer diameter of 9.5 mm, an inner diameter of 2.0955 mm, and a height of 8 mm under the conditions of a load of 325 gf and a temperature of 270 ° C. The amount of resin extruded (g) was measured. The same measurement was repeated 3 times, and the average value was defined as MFR.

(3) Average fiber diameter of ultrafine fibers A cross section perpendicular to the thickness direction including the ultrafine fibers of the polishing cloth was observed with a scanning electron microscope (VE-7800 manufactured by SEM Keyence Corporation) at a magnification of 3000, and a field of view of 30 μm × 30 μm The diameter of 50 single fibers extracted at random was measured. However, this was performed at three locations, the diameters of a total of 150 single fibers were measured, and the average value was calculated by rounding off the numbers after the decimal point.
In addition, when the fiber diameter exceeds 10 micrometers, the said fiber shall be excluded from the measurement object of an average fiber diameter as what does not correspond to an ultrafine fiber.
When the ultrafine fiber has an irregular cross section, first, the cross sectional area of the single fiber is measured, and the diameter of the single fiber is calculated by calculating the diameter when the cross section is regarded as a circle.

(4) The number of fiber bundles in the cross section perpendicular to the thickness direction of the polishing cloth The cross section (surface parallel to the surface of the polishing cloth) perpendicular to the thickness direction of the polishing cloth is removed by a half-cutting machine having an endless band knife (excluding the reinforcing layer). It cut out in the middle of the thickness direction and photographed 100 times with SEM. The obtained photograph was magnified 4 times, and the number of fiber bundle cross sections per 0.5 mm × 0.5 mm was counted and converted into the number of cut ends per 1 mm ^{2 of} area. This was performed at 10 locations, and the average value was calculated.

(5) Cut ends of fiber bundles existing on the surface of the polishing cloth The surface of the polishing cloth was photographed with a SEM at a magnification of 100 times, and the resulting photograph was magnified four times to obtain an ultrafine size of 0.5 mm × 0.5 mm. The number of cut ends of the fiber bundle was counted and converted into the number of cut ends per area of 1 mm ² . This was performed at 10 locations, and the average value was calculated.

(6) Number of fiber bundles in a cross section parallel to the thickness direction of the polishing cloth A cross section parallel to the thickness direction of the polishing cloth was cut out and photographed with a SEM at a magnification of 50 times. The obtained photograph was magnified 4 times, and the number of fiber bundles existing in a range of 1 cm in width on a straight line orthogonal to the thickness direction was counted, and an average value at 10 locations was calculated.

(7) Polishing process A polishing cloth was used as a tape having a width of 40 mm.
As an object to be polished, a disk that was subjected to Ni-P plating treatment on an aluminum substrate, polished, and controlled to have an average surface roughness of 0.2 nm was used.
A slurry of free abrasive grains in which single crystal diamond particles having a primary particle diameter of 1 to 10 nm were clustered to an average diameter of 100 nm was dropped onto the surface of the polishing cloth and polished for 20 seconds at a tape running speed of 5 cm / min. This was done on both sides of each disk.

(8) Substrate surface roughness
Measured based on JIS B 0601: 2001. Using a surface roughness measuring machine (TMS-2000 manufactured by Schmidt Measurement System Co., Ltd.), the average roughness was measured at 10 locations on the surface of the disk substrate sample after polishing, and the measured values at 10 locations were averaged. The surface roughness was calculated. The lower the value, the higher the performance.

(9) Number of scratch points
Using the optical surface analyzer (Candela 6100) as a measurement target on both surfaces of the five substrates after polishing, that is, the total area of the surface of 10 substrates, the number of scratches was measured using a groove having a depth of 2 nm or more as a scratch. The average value of the measured values was evaluated. The lower the value, the higher the performance.

[Example 1]
(raw cotton)
(Sea component / island component)
Nylon 6 having a melting point of 220 ° C. and MFR 10.5 was used as an island component, and copolymerized polystyrene (co-PSt) obtained by copolymerizing 22 mol% of 2-ethylhexyl acrylate having a melting point of 53 ° C. and MFR 12 was used as a sea component.

(Spinning / drawing)
Using the sea and island components described above, using a 376 island / hole sea-island type composite die, spinning temperature 285 ° C., island / sea mass ratio 40/60, discharge rate 1.3 g / min / hole, spinning speed 1000 m / Melt spun in minutes. Next, it is stretched 3.0 times in a liquid bath at 85 ° C., crimped by an indentation type crimper, cut, and a raw material of sea-island type composite fiber having a fineness of 3.6 dtex and a fiber length of 51 mm is obtained. Obtained.

(Extra-fine fiber generation type nonwoven fabric)
Using the raw cotton, a laminated web was formed through a card and a cross wrapper process. Then, a single needle total barb depth 0.08mm at planting elaborate needle punching machine, needle depth 8 mm, at a punching number 10500 present / cm ² needle punched basis weight 695 g / ^{m 2,} an apparent density of 0.22 g / A cm ³ ultrafine fiber-generating fiber nonwoven fabric was prepared.

(Polishing cloth)
The ultrafine fiber generating fiber nonwoven fabric was subjected to hot water shrinkage at 95 ° C., and then 24% by mass of polyvinyl alcohol was added to the fiber mass, and then dried.
To this non-woven fabric, 20% by mass of a solid content with respect to the mass of fiber is added to a polyurethane whose polymer diol is 75% by mass of polyether and 25% by mass of polyester, and the polyurethane is obtained by using a 30% DMF aqueous solution at a liquid temperature of 35 ° C. Was solidified, and DMF and polyvinyl alcohol were removed with hot water at about 85 ° C. Then, the half-cut surface was half-cut with a half-cutting machine having an endless band knife, and the half-cut surface was ground in three stages with a JIS # 600 sandpaper to form napped hairs to produce a polishing cloth.
The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 0.75 μm, a thickness of 0.53 mm, a basis weight of 170 g / m ² , and an apparent density of 0.32 g / cm ³ .

[Example 2]
(raw cotton)
The same one as used in Example 1 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the number of needle punches was 13500 / cm ² .

(Polishing cloth)
A polishing cloth was obtained in the same manner as in Example 1 except that the above ultrafine fiber-generating fiber nonwoven fabric was used.
The obtained polishing cloth had a thickness of 0.52 mm, a basis weight of 156 g / m ² , and an apparent density of 0.30 g / cm ³ .

[Example 3]
(raw cotton)
The same one as used in Example 1 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the number of needle punches was 4500 / cm ² .

(Polishing cloth)
A polishing cloth was obtained in the same manner as in Example 1 except that the above ultrafine fiber-generating fiber nonwoven fabric was used.
The obtained polishing cloth had a thickness of 0.55 mm, a basis weight of 170 g / m ² , and an apparent density of 0.31 g / cm ³ .

[Comparative Example 1]
(raw cotton)
The same one as used in Example 1 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the number of needle punches was 1500 / cm ² .

(Polishing cloth)
A polishing cloth was obtained in the same manner as in Example 1 except that the above ultrafine fiber-generating fiber nonwoven fabric was used.
The obtained polishing cloth had a thickness of 0.55 mm, a basis weight of 175 g / m ² , and an apparent density of 0.32 g / cm ³ .

[Example 4]
(raw cotton)
A sea-island type composite fiber having a fineness of 2.8 dtex and a fiber length of 51 mm was used in the same manner as in Example 1 except that a discharge amount of 1.0 g / min / hole was used using a sea-island type composite base having 36 islands / hole. Obtained raw cotton.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the raw cotton was used.

(Polishing cloth)
A polishing cloth was obtained in the same manner as in Example 1 except that the above ultrafine fiber-generating fiber nonwoven fabric was used.
The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 2.11 μm, a thickness of 0.55 mm, a basis weight of 167 g / m ² , and an apparent density of 0.30 g / cm ³ .

[Comparative Example 2]
(raw cotton)
A sea island type composite fiber having a fineness of 5.6 dtex and a fiber length of 51 mm was used in the same manner as in Example 1 except that a sea island type composite base with 16 islands / hole was used and the discharge rate was 2.0 g / min / hole. Obtained raw cotton.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the raw cotton was used.

(Polishing cloth)
A polishing cloth was obtained in the same manner as in Example 1 except that the above ultrafine fiber-generating fiber nonwoven fabric was used.
The obtained polishing cloth had an average fiber diameter of 3.10 μm, a thickness of 0.56 mm, a basis weight of 177 g / m ² , and an apparent density of 0.32 g / cm ³ .

  The disc after polishing processing lacked surface uniformity.

[Comparative Example 3]
(raw cotton)
(Sea component / island component)
The same components as those used in Example 1 were used as the sea component and the island component, respectively.

(Spinning / drawing)
The sea component / island component was chip-blended at an island / sea mass ratio of 30/70, and melt-spun at a discharge rate of 1.3 g / min / hole and a spinning speed of 600 m / min. Subsequently, it was stretched 2.5 times in a liquid bath at 85 ° C., crimped by a push-type crimper, and cut to obtain a raw cotton fiber having a fineness of 4.3 dtex and a fiber length of 51 mm.

(Extra-fine fiber generation type nonwoven fabric)
A polishing cloth was obtained in the same manner as in Example 1 except that the raw cotton was used.
The obtained abrasive cloth had an average fiber diameter of 0.28 μm, a thickness of 0.54 mm, a basis weight of 172 g / m ² , and an apparent density of 0.32 g / cm ³ .

  The disc after polishing had a undulation on the surface of the disc due to a low grinding amount and lacked uniformity.

  The polishing cloth of the present invention is suitably used when an aluminum alloy substrate or glass substrate used for a magnetic recording disk is polished or cleaned with an ultra-high precision finish.

Claims (4)

It has a nonwoven fabric in which bundles of ultrafine fibers having an average fiber diameter of 0.3 to 3.0 μm are entangled, and in the cross section orthogonal to the thickness direction of the polishing cloth, the cross section of the ultrafine fiber bundles is 50 to 1000 A polishing cloth characterized by the presence of / mm ² . Cut ends of the microfine fiber bundle in at least one side surface is present 10 to 150 pieces / mm ^2, a polishing cloth according to claim 1. The polishing cloth according to claim 1 or 2, wherein 80 to 500 ultrafine fiber bundles are present per 1 cm width in a cross section parallel to the thickness direction of the polishing cloth. The polishing cloth according to any one of claims 1 to 3, comprising an elastic polymer.