JP2008254136A - Polishing cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance polishing cloth capable of eliminating scratch and minute projections by having microfibers of nano fiber level on its surface, when used for accurate polishing of a hard disc and the like. <P>SOLUTION: The polishing cloth is manufactured by electrostatic spinning method; and composed of a microfiber structure having an average fiber diameter of 1.0 nm to 1.0 μm, and a composite fiber structure in which a microfiber structure having an average fiber diameter of 0.50 to 10 μm are laminated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polishing cloth that can be suitably used when performing polishing and / or cleaning processing in finishing processing of a semiconductor wafer, a magnetic recording disk, etc., by dispersing nanofiber-level ultrafine fibers on the surface, The present invention relates to a polishing cloth having excellent smoothness and high polishing performance.

  2. Description of the Related Art In recent years, magnetic recording media such as magnetic disks tend to have a significantly reduced flying height (flying height) of a magnetic head with an increase in capacity and storage density. Therefore, if there is an abnormal defect such as a protrusion on the surface of the magnetic disk, the magnetic head and the abnormal defect come into contact with each other, causing a head crash and causing a scratch on the disk surface. Further, even a minute protrusion that does not cause a head crash leads to an error that occurs when reading and writing information due to contact with the magnetic head.

  As a method of manufacturing a magnetic recording medium, a magnetic material is formed by sputtering after slurry grinding using a polishing pad is performed on an aluminum alloy substrate or a glass substrate. Generally, the surface of the disk after slurry grinding using a polishing pad made of rigid polyurethane foam or polyurethane impregnated nonwoven fabric has many scratches and minute protrusions and is not smooth. In order to improve the smoothness by removing the surface, grinding has been performed by attaching free abrasive grains to the surface of a tape-like polishing cloth made of a nonwoven fabric or a woven fabric. For processing, using a polishing cloth as a tape, while the aluminum alloy substrate or glass substrate is continuously rotated, the abrasive tape is pressed against the substrate and reciprocated in the radial direction of the substrate to continuously run the polishing tape. Let At that time, by supplying a slurry containing loose abrasive grains between the polishing tape and the substrate, the loose abrasive grains are gripped in a finely dispersed state on the fibers on the polishing tape surface, and polishing is performed by contacting this with the substrate. Is something that progresses.

  In particular, in the manufacture of a conventional magnetic recording disk of the longitudinal (in-plane) magnetic recording system, fine constrictions are formed substantially concentrically on the substrate surface of the recording disk by slurry grinding with a tape-like polishing cloth. When the metal magnetic layer is formed on the disk substrate, the direction of crystal growth of the magnetic material is controlled, so that the coercive force in the recording direction is improved and the recording density can be increased. Slurry grinding in this longitudinal magnetic recording system is called texture processing.

  On the other hand, recently, as the recording method of the magnetic recording disk has shifted from the conventional longitudinal magnetic recording method to the perpendicular magnetic recording method, smoothing is achieved by slurry grinding using a tape-like polishing cloth and / or cleaning processing without using a slurry. There is a growing demand for improved performance. At this time, in order to smooth the surface, it is necessary to suppress the formation of fine streaks on the disk substrate surface required in the longitudinal magnetic recording method.

  When performing surface treatment to satisfy low flying height of the magnetic head by slurry grinding and / or cleaning processing using a tape-like polishing cloth, it supports the recent rapid increase in recording density for high recording capacity. In order to achieve this, it is required to achieve a substrate surface roughness of 0.2 nm or less and to minimize scratches on the substrate surface called scratch defects, and a polishing cloth that can meet the demand is desired. Yes. In order to reduce the substrate surface roughness, various proposals have been made to impregnate the nonwoven fabric with a polymer elastic body to provide cushioning properties in order to minimize the fibers constituting the nonwoven fabric and minimize scratches on the substrate surface. Yes.

For example, an abrasive cloth made of a polyamide ultrafine fiber nonwoven fabric of 0.03 dtex or less (Patent Document 1) has been proposed, and the finest ones in the examples use ^10-4 order ultrafine fibers. However, in processing using an abrasive cloth, the surface roughness is about 0.4 nm, and in order to achieve a further reduction in surface roughness, ultrafine fibers at the nanofiber level are required.

As an abrasive cloth using nanofiber level ultrafine fibers, for example, Patent Document 2 discloses an abrasive cloth made of ultrafine fibers of 1 × 10 ⁻⁸ to 4 × 10 ⁻⁴ dtex using polymer alloy fibers. . However, the ultrafine fibers of the polishing cloth are in a bundled state, the properties of the bundled fibers are dominant, and the superiority of the ultrafine fibers, such as a reduction in surface roughness, cannot be fully exhibited. (The substrate surface roughness in the examples is about 0.21 to 0.30 nm). Therefore, there has been a strong demand for a polishing cloth that can satisfy the smoothness and minimum scratches and protrusions required in recent perpendicular recording type magnetic recording disks.
JP 2002-79472 A JP 2005-329534 A

  An object of the present invention is to provide a high-performance polishing cloth that can achieve removal of scratches and minute protrusions by having nanofiber-level ultrafine fibers on the surface in precision polishing applications such as hard disks. That is.

The present invention employs the following means in order to solve such problems. That is,
(1) A composite fiber structure in which an ultrafine fiber structure having an average fiber diameter of 1.0 nm to 1.0 μm and a fine fiber structure having an average fiber diameter of 0.50 to 10 μm, which are manufactured by an electrostatic spinning method, are laminated. A polishing cloth comprising a body.

  (2) Polishing characterized by comprising an ultrafine fiber structure having an average fiber diameter of 1.0 nm to 1.0 μm, produced by an electrospinning method, and a composite structure in which a polymer elastic body layer is laminated. cloth.

  (3) The abrasive cloth according to (1), wherein the composite fiber structure includes a polymer elastic body.

  (4) The polishing cloth according to any one of (2) and (3), wherein the elastic polymer is polyurethane.

  (5) The surface of the fine fiber structure and the polymer elastic body has a hardness measured based on JIS K-6253A of 30 to 60 °, according to the above (2) to (4) The polishing cloth in any one.

  (6) The polishing cloth according to any one of (1) to (5), wherein a reinforcing layer is laminated on one side.

  Since the polishing cloth of the present invention is excellent in the dispersibility and uniformity of the ultrafine fibers on the surface of the polishing cloth, slurry grinding and / or slurry using a tape-like polishing cloth on the surface of a substrate such as a magnetic recording disk. Provides a high-performance polishing cloth that can minimize the generation of scratches and minute protrusions in the cleaning process that does not use, and that can satisfy the fine streaking requirements of perpendicular recording disks. It can be done.

  Hereinafter, the present invention will be described in detail together with preferred embodiments.

  In the present invention, the ultrafine fiber structure is a structure made of ultrafine fibers having an average fiber diameter of 1.0 nm to 1.0 μm, and the fine fiber structure is made of fine fibers having an average fiber diameter of 0.50 to 10 μm. The structure is not particularly limited.

  The average fiber diameter of the ultrafine fiber structure layer used in the polishing cloth of the present invention is preferably 1.0 nm to 1.0 μm from the viewpoint of fiber strength on the polishing cloth surface and gripping ability of the abrasive grains. By setting the thickness to 1.0 nm or more, sufficient fiber strength necessary for grinding can be obtained, and the abrasive grains can be accurately grasped. On the other hand, when the thickness is 1.0 μm or less, the abrasive grains can be finely dispersed, and the abrasive grain distribution on the surface of the polishing cloth can be made uniform. A more preferable range of the average fiber diameter is 1.0 nm to 0.50 μm. In addition, an average fiber diameter says the value measured with the measuring method mentioned later. That is, using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) with a cross section cut in the thickness direction of the polishing cloth as an observation surface, the fiber diameter of 300 fibers is measured with three significant digits, An average value using this as a population is calculated with two significant digits, and this average value is taken as the average fiber diameter. When the cross-sectional shape of the fiber is non-circular, after calculating the cross-sectional area, the diameter of a circle having the same area is regarded as the fiber diameter.

  It is difficult to obtain ultrafine fibers having an average fiber diameter of 1.0 nm to 1.0 μm dispersed on the surface of the polishing cloth by a simple direct spinning method. Also, it seems that the papermaking method using ultra-fine short fibers seems to be acceptable, but there are problems in using them in abrasive cloths from the viewpoint of fiber dropout due to short fiber length and productivity during processing. . On the other hand, the sea-island type composite spinning method or the method using ultrafine fiber generation type fibers such as polymer blend and chip blend is preferable for abrasive cloth use. However, the fibers tend to be bundled, and electrostatic properties can be given priority to the dispersibility of ultrafine fibers. It is more preferable to use a spinning method.

  The polymer of ultrafine fibers having an average fiber diameter of 1.0 nm to 1.0 μm used in the polishing cloth of the present invention is not particularly limited as long as it can be spun by an electrostatic spinning method. For example, aromatic polyesters such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, aliphatic such as polylactic acid (PLA), polycaprolactone, polybutylene succinate, polyethylene succinate Polyester, Nylon 6 (N6), Nylon 66, Nylon 11, Nylon 12, Nylon 610, Nylon 612 and other polyamides, Polymethyl methacrylate, Polyethyl methacrylate and other methacrylates, Poly normal propyl acrylate, Poly normal butyl acrylate, Acrylates such as polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, and polybutyl isocyanate , Polyvinyl chloride, polyacrylonitrile, polystyrene, and the like copolymers thereof. Of these, polyamide-based, polyester-based, polyacrylonitrile-based, and the like are preferable because of the ease of spinning and the polishing performance with the resulting fibers. Further, other polymers and other compounds may be used in combination as long as the performance of the polymer is not impaired.

  In addition to the ultrafine fiber structure described above, the abrasive cloth of the present invention can obtain an appropriate cushioning property by having a fine fiber structure, and obtain a high polishing performance that cannot be obtained only with an ultrafine fiber assembly. Is possible. As a general structure, an ultrafine fiber aggregate and a fine fiber aggregate are laminated, and a structure having the ultrafine fiber aggregate on the surface of the polishing cloth is preferable. The structure of the fine fiber aggregate is not particularly limited, but a woven or knitted fabric or nonwoven fabric made of polyester, polyamide, polyolefin or the like is preferably used as the base material.

  The average fiber diameter of the fine fiber structure is preferably in the range of 0.50 to 10 μm. A thickness of 0.50 μm or more is preferable because sufficient strength and cushioning properties can be obtained. Further, when the thickness is 10 μm or less, the flexibility of the fine fiber structure layer can be obtained, and even when the fine fibers are exposed on the surface of the polishing cloth, it is difficult to cause abnormal defects such as scratches, which is preferable.

  The polishing cloth of the present invention may contain a polymer elastic body for the purpose of improving cushioning properties. In general, it is preferable to have an ultrafine fiber layer on the surface of the polishing cloth and a polymer elastic body layer as a non-polished surface. The polymer elastic body layer may be impregnated into a sheet-like material such as a nonwoven fabric, or may be only a sheet-like polymer elastic body obtained by a dry method or the like. The polymer elastic body to be used is not particularly limited. For example, polyurea, polyurethane / polyurea elastomer, polyacrylic resin, acrylonitrile / butadiene elastomer, styrene / butadiene elastomer, etc. can be used. A polyurethane-based elastomer such as an elastomer is preferred.

  Polyurethanes can use polyester-based, polyether-based, polycarbonate-based diols, or copolymers thereof for the polyol component. Moreover, as a diisocyanate component, aromatic diisocyanate, alicyclic isocyanate, aliphatic isocyanate, etc. can be used.

  The weight average molecular weight of the polyurethane is preferably 50,000 to 300,000, more preferably 100,000 to 250,000. By setting the weight average molecular weight to 50,000 or more, it is possible to maintain the strength of the obtained sheet-like material and to prevent the ultrafine fibers from falling off. Moreover, by setting it as 300,000 or less, the increase in the viscosity of a polyurethane solution can be suppressed and it can make it easy to impregnate a nonwoven fabric.

  In addition, it is preferable to use polyurethane as the main component of the polymer elastic body, but as a binder, it does not impair the performance and the uniform dispersion state of the napped fibers, and polyester resin, polyamide resin, polyolefin resin, etc., acrylic resin , Ethylene-vinyl acetate resin, etc. may be included, and if necessary, colorants, antioxidants, antistatic agents, dispersants, softeners, coagulation modifiers, flame retardants, antibacterial agents, deodorants, etc. Additives may be blended.

  In the present invention, the amount of the polymeric elastic body applied to the sheet-like material such as the nonwoven fabric is 10 to 200% by weight as a solid content with respect to the weight of the fiber in consideration of the denseness and cushioning properties of the polishing cloth surface fibers. A range is preferred. Preferably it is the range of 20-100 weight%.

  The fine fiber assembly layer and the polymer elastic layer of the present invention preferably have a hardness of 30 to 60 ° as measured based on JIS K-6253A. By setting the hardness to 30 ° or more, the pressing force of the abrasive grains is sufficiently transmitted, and by setting the hardness to 60 ° or less, it is possible to suppress scratch defects and achieve low surface roughness.

When the polishing cloth of the present invention is subjected to a polishing process in the form of a tape or a pad, if a large dimensional change occurs, the substrate surface cannot be uniformly polished. invention fine fiber aggregate layer used, and it is preferable that the basis weight of the elastic polymer layer is 50 to 2000 g / ^{m 2,} more preferably from 100 to 1000 g / ^{m 2,} more preferably 150~600g / M ² range. From the same viewpoint, the fine fiber aggregate and the polymer elastic layer of the present invention preferably have a thickness in the range of 0.1 to 5 mm, more preferably in the range of 0.2 to 3 mm. In order to obtain uniform workability, the apparent density is preferably in the range of 0.2 to 0.9 g / cm ³ , more preferably in the range of 0.3 to 0.8 g / cm ³ .

Incidentally, preferably in the range of 0.3 to 10 / ^{m 2} as a weight per unit area of the ultrafine fibrous aggregate layer of the polishing cloth surface. When it is 0.3 g / m ² or more, sufficient performance as a fine fiber assembly layer can be exhibited, and when it is 10 g / m ² or less, delamination that is laminated with the ultrafine fiber assembly layer, etc. Can be prevented.

  The basis weight of each layer of the present invention was measured according to JIS L 1096 8.4.2 (1999). As for the apparent density, the thickness of each aggregate layer was measured at 10 arbitrary points with a dial thickness gauge (manufactured by Ozaki Mfg. Co., Ltd., trade name “Peacock H”), and the average value was calculated. Calculated by dividing by thickness.

  In the present invention, from the viewpoint of suppressing scratch defects, the content of the metal or metal compound contained in the polishing cloth is preferably 100 ppm or less, preferably 30 ppm or less, as the weight of the metal element with respect to the total weight of the polishing cloth. Is more preferable, and it is still more preferable not to contain at all. If it is 100 ppm or less, the generation of scratch defects due to the contact of the metal or metal compound with the substrate surface can be suppressed, which is preferable.

  Examples of the metal or metal compound contained in the polishing cloth include iron, iron oxide, and titanium dioxide used as an additive for fiber polymers.

  Furthermore, from the viewpoint of suppressing the occurrence of processing irregularities and scratch defects at the time of polishing, a method of adhering a reinforcing layer to the back surface of the surface having fine fibers of the polishing cloth is preferably applied to the polishing cloth made of the composite fiber structure. Used.

  The reinforced layer is not particularly limited as long as dimensional stability is obtained, and it is preferable to use a woven or knitted fabric, a nonwoven fabric using heat-bonding fibers, or a film-like material. Among these, in order to perform high-precision polishing, it is more preferable to use a film-like material that is uniform in thickness and physical characteristics.

  As a raw material used as a film here, what has film shape, such as a polyolefin type, a polyester type, and a polyphenyl sulfide type, can be used. In consideration of versatility, it is preferable to use a polyester film. When a reinforcing layer made of a film is provided, it is necessary to satisfy all of the form stability, cushioning properties and fitability to the substrate surface of the polishing cloth during polishing, so the thickness balance with the sheet-like material made of nonwoven fabric It is important to take The finished thickness of the sheet-like material made of nonwoven fabric is preferably 0.2 mm or more, and more preferably in the range of 0.2 to 2.0 mm from the viewpoint of productivity. Therefore, the thickness of the film is preferably 20 to 100 μm. When the thickness of the sheet-like material made of nonwoven fabric is less than 0.2 mm, a reinforcing layer is necessary to suppress dimensional changes during polishing. On the other hand, if the thickness of the film layer is less than 20 μm, the dimensional change at the time of polishing cannot be suppressed, and if it exceeds 100 μm, the rigidity of the entire polishing cloth becomes too high, and as a result, the occurrence of scratches cannot be suppressed. Therefore, it is not preferable.

  Next, the manufacturing method of the polishing cloth of the present invention will be described in detail.

  The ultrafine fiber structure of the present invention is produced by an electrospinning method. The ultrafine fibers produced by the electrospinning method are preferable because they do not easily form bundles and the ultrafine fibers are dispersed, so that the abrasive grains can be accurately grasped in the polishing process. The electrospinning method is a conventionally known method, in which a solution in which a fiber-forming compound is dissolved is supplied from a nozzle or the like and stretched by applying an electric field to form a fiber.

  Next, the electrostatic spinning method will be specifically described.

  First, a spinning solution in which an ultrafine fiber constituent material is dissolved is prepared. The solvent of the spinning solution is not particularly limited as long as it dissolves the ultrafine fiber constituent material. For example, water, acetone, methanol, ethanol, propanol, isopropanol, benzyl alcohol, 1,4-dioxane, Phenol, toluene, benzene, cyclohexane, cyclohexanone, tetrahydrofuran, dimethyl sulfoxide, methylene chloride, chloroform, trichloroethane, N, N-dimethylformamide, N, N-dimethylacetamide, ethylene carbonate, diethyl carbonate, propylene carbonate, acetonitrile, etc. However, it is not limited to these solvents, and can be used as a mixed solvent of two or more kinds. In order to improve the solubility of the polymer and the spinning stability, an inorganic salt, an organic salt, a plasticizer, or the like may be added to the solvent. In addition, the kind of polymer dissolved in these solvents is as described above.

  The concentration of the polymer in the solution is preferably 1 to 40% by weight. By setting it to 1% by weight or more, it is possible to secure a concentration sufficient to form a fiber structure, and by setting it to 40% by weight or less, it is possible to control the average fiber diameter of the obtained fibers to the nanofiber level. Become. More preferably, it is in the range of 2 to 30% by weight.

  A spinning solution is supplied to a nozzle, spun from the nozzle, and an electric field is applied to the spun spinning solution to form ultrafine fibers. Since the diameter (inner diameter) of the nozzle for spinning the spinning solution affects the average diameter of the ultrafine fibers, it is preferably about 0.1 to 2.0 mm in order to obtain ultrafine fibers with a fiber diameter of 1.0 μm or less. It is preferable.

  After spinning the spinning solution from the nozzle, an electric field is applied to the spinning solution to draw and make it ultrafine. Although the magnitude of the electric field is not particularly limited, it is preferably 0.1 to 5 kV / cm in order to make the diameter of the ultrafine fiber within a desired range. Fiber formation is possible by setting it to 0.1 kV / cm or more, and it is preferable because it can prevent dielectric breakdown of air by setting it to 5 kV / cm or less.

  The electric field can be applied, for example, by providing a potential difference between the nozzle and the integrated body. The applied voltage is not particularly limited as long as the above-described electric field strength can be obtained, but is preferably in the range of 5 to 50 kV, more preferably in the range of 5 to 30 kV.

  An ultrafine fiber assembly layer in which the ultrafine fibers are laminated on a collector can be formed. The collector is not particularly limited as long as it can collect ultrafine fibers. For example, a conductive material such as a metal or a non-conductive material such as a nonwoven fabric, a woven or knitted fabric, a net, a drum, or a belt can be used. It is.

  The polishing cloth of the present invention provides nanofiber-level ultrafine fibers on the surface by providing a cushion layer made of fine fiber aggregates having an average fiber diameter of 0.50 to 10 μm in addition to the above-described ultrafine fiber aggregate layers. It is possible to obtain a high polishing performance having excellent smoothness, cushioning properties and dimensional stability.

  The fine fiber aggregate layer is not particularly limited, but a woven or knitted fabric, a non-woven fabric, or the like is preferably used, but a non-woven fabric is preferable from the viewpoint of the undulation of the entire aggregate layer, uniformity of thickness / weight per unit area, cushioning property, etc. Used for.

  The method for obtaining the nonwoven fabric constituting the fine fiber structure in the present invention is not particularly limited. In order to obtain fine fibers having an average fiber diameter of 0.50 to 10 μm, single-component spinning or sea-island composite Known ultra-thinning techniques such as spinning, split-type composite spinning, and electrostatic spinning can be used. Among these, fine fibers obtained from sea-island type composite spinning are preferable from the viewpoint of reducing the fiber diameter of the obtained fine fibers. In addition, the structure of the nonwoven fabric is obtained by forming a laminated web in which short fibers obtained through spinning, drawing, crimping, and cutting are arranged in the width direction using a card and a cross wrapper, and then performing needle punching. The short fiber nonwoven fabric obtained, the long fiber nonwoven fabric obtained from the spun bond or melt blow method, the nonwoven fabric obtained by the papermaking method, the nonwoven fabric obtained by the electrostatic spinning method, etc. can be used. Among these, a short fiber nonwoven fabric is preferably used from the viewpoints of smoothness as a polishing cloth, unevenness per unit area, dimensional stability, cushioning properties, and the like.

  The method of entanglement of the fiber web of the short fiber nonwoven fabric is not particularly limited, but methods such as needle punching and water jet punching can be appropriately combined.

The number of punches in the needle punching process is preferably 500 to 8000 / cm ² from the viewpoint of achieving a dense surface state by high entanglement of fibers. The density of the surface fiber can be obtained by setting it to 500 lines / cm ² or more, and it is preferable to set it to 8000 lines / cm ² or less because deterioration of workability and strength reduction due to fiber damage can be prevented. . The fiber density of the composite fiber nonwoven fabric after needle punching is preferably in the range of 0.20 to 0.50 g / cm ³ from the viewpoint of densification of the number of surface fibers. When performing a water jet punching process, it is preferable to perform water in the state of a columnar flow. In order to obtain a columnar flow, generally, a method of ejecting from a nozzle having a diameter of 0.05 to 1.0 mm at a pressure of 1 to 60 MPa is suitably used. From the viewpoint of densification, the composite fiber nonwoven fabric obtained in this way may be contracted by dry heat or wet heat, or both, and further densified.

  The method of developing ultrafine fibers from the sea-island type composite fibers that make up the fine fiber aggregates, that is, the fine fiber generation processing varies depending on the types of components to be removed (sea components made of easily soluble polymers), but polyethylene, polystyrene, etc. In the case of polyolefins such as these, an organic solvent such as toluene or trichlorethylene, and in the case of PLA or copolymer polyester, a method of immersing and constricting with an alkaline aqueous solution such as sodium hydroxide can be preferably used.

  The abrasive cloth of the present invention is either before the fine fiber assembly layer is subjected to ultrafine fiber treatment and / or after the fine fiber aggregate layer is subjected to ultrafine fiber treatment, or after being laminated with the ultrafine fiber aggregate layer. In the process, a polymer elastic body mainly composed of polyurethane may be provided. Such a polymer elastic body has a role of surface unevenness, a cushion for vibration absorption, fiber shape maintenance, and the like. It is excellent in fit and the effect of suppressing scratches on the surface of the workpiece.

  As a method for applying such polyurethane to the nonwoven fabric, a method of applying polyurethane or solidifying after impregnation can be appropriately employed. Among them, from the viewpoint of processability, wet nonwoven solidification is carried out after impregnating the polyurethane solution into the nonwoven fabric. Is preferably used.

  The polymer elastic body to be used is as described above, and N, N'-dimethylformamide, dimethyl sulfoxide, or the like can be preferably used as a solvent used for imparting the polymer elastic body. Further, an aqueous polyurethane dispersed as an emulsion in water may be used. The polymer elastic body is applied to the nonwoven fabric by immersing the nonwoven fabric in a polymer elastic body solution dissolved in a solvent, and then dried to substantially solidify and solidify the polymer elastic body. In drying, you may heat at the temperature which does not impair the performance of a nonwoven fabric and a polymeric elastic body.

  The polishing cloth of the present invention can be formed by, for example, calendering using a flat roll or the like after separately manufacturing the above-described ultrafine fiber aggregate layer and fine fiber aggregate layer and / or polymer elastic body layer. It is possible to integrate by pressing and compressing. At the time of calendering, heating may be performed within a range that does not impair the performance of the ultrafine fiber layer, or heating may not be performed. This pressure compression process can be carried out in either a dry or wet state, but in the dry state, it may cause adhesion of the surface fibers to the roll and fusion of only the surface part. It is preferably performed in a wet state. In the wet state, the thermal conductivity is higher than that in the dry state, and as a result, the entire polishing cloth can be compressed uniformly, which is preferable.

  As a method of further adhering the reinforcing layer to the polishing cloth comprising the composite fiber structure of the present invention, any method can be adopted, such as a thermocompression bonding method, a frame lamination method, or an adhesive layer provided between the reinforcing layer and the sheet-like material. As the adhesive layer, those having rubber elasticity such as polyurethane, styrene butadiene rubber (SBR), nitrile butadiene (NBR), polyamino acid and acrylic adhesive can be used. In view of cost and practicality, an adhesive such as NBR or SBR is preferable. As a method for applying the adhesive, an emulsion or a method of applying the adhesive to a sheet in a latex state is preferably used.

  As a method for performing polishing using the polishing cloth of the present invention, from the viewpoint of processing efficiency and stability, the polishing cloth is cut into a tape having a width of 30 to 50 mm and used as a polishing tape.

  A method of polishing an aluminum alloy magnetic recording disk or a glass magnetic recording disk using the polishing processing tape and a slurry containing free abrasive grains, and cleaning of the disk using the processing tape and an aqueous cleaning agent Processing is the preferred method. As a polishing condition, a slurry in which abrasive particles such as diamond fine particles and colloidal silica are dispersed in an aqueous dispersion medium is preferably used. In addition, from a viewpoint of the retainability and dispersibility of abrasive grains, the primary abrasive grain size suitable for the ultrafine fibers constituting the polishing cloth of the present invention is preferably 1 to 200 nm, more preferably 1 to 100 nm. Moreover, you may use the abrasive grain which consists of a secondary particle which the primary abrasive grain clustered.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. The evaluation methods used in the examples and the measurement conditions will be described below.

(1) Sulfuric acid relative viscosity of polymer The components other than the fine fiber component are removed from the polishing cloth by dissolution or the like, only the fine fiber is taken out, and 0.25 g of the fine fiber is precisely weighed with a direct balance (0.25 ± 0. 005g). Next, the precisely weighed sample is dissolved in 25 ml of concentrated sulfuric acid to obtain a sample solution. Next, 15 ml of the sample solution was injected into a viscosity tube (with a concentrated sulfuric acid falling time of 100 ± 20 seconds) set in a thermostat heated to 25 ± 0.5 ° C., and then the dropping time of the sample solution Measure. This operation is repeated three times to obtain an average value T. The same operation is repeated three times for concentrated sulfuric acid in which the sample is not dissolved, the average value T0 is determined, and T / T0 is defined as the sulfuric acid relative viscosity.

(2) Average fiber diameter Using a scanning electron microscope (SEM) or transmission electron microscope (TEM) as an observation surface, a cross-section of the polishing cloth cut in the thickness direction is observed, and the fiber diameter of 300 fibers is 3 significant figures Then, the average value of this as a population is calculated with two significant figures, and this average value is taken as the average fiber diameter. When the cross-sectional shape of the fiber is non-circular, after calculating the cross-sectional area, the diameter of a circle having the same area is regarded as the fiber diameter.
TEM equipment: H-7100FA type SEM equipment manufactured by Hitachi, Ltd .: VE-7800 type, manufactured by Keyence Corporation (3) JIS L 1096 8.4.2 (1999) for each of the ultrafine fibers and the fine fiber aggregates ) And measured.

(4) Apparent density The thickness of the fineness aggregate was measured at 10 arbitrary points with a dial thickness gauge (manufactured by Ozaki Mfg. Co., Ltd., trade name “Peacock H”), and the average value was calculated. By dividing the basis weight obtained in (3) by the thickness, the apparent density was calculated with two significant figures.

(5) Hardness of Fine Fiber Assembly Layer and Polymer Elastic Body Layer Ten specimen pieces having a size of 7 cm × 7 cm were prepared based on the provisions of JIS K-6253A. One of them was attached to a CL-150 low-pressure load hardness meter equipped with an ASKER A-type hardness sensor from Kobunshi Keiki Co., Ltd., and the hardness was measured at room temperature of 20 ° C. and humidity of 60%. The hardness of 10 sheets in total was measured by the same method, and the average value of the obtained sample hardness was evaluated as the hardness of the fine fiber assembly layer and the polymer elastic body layer.

(6) Substrate Surface Roughness Using an atomic force microscope AFM (NanoScope IIIaAFM Dimension 3000 stage system manufactured by Digital Instruments), any number of 10 surfaces on each side of five disk substrate samples after polishing, that is, a total of 10 surfaces Two areas (the observation area per area is an area of 5 μm in the radial direction on the disk surface × 5 μm in the circumferential direction) were extracted. Next, a cross-sectional profile with one point for each of these 10 locations and a cross-sectional profile with the horizontal axis in the thickness direction of the disk as a radial direction is arbitrarily extracted, and each of the obtained cross-sectional profiles conforms to JIS B 0601 (2001 edition). The arithmetic average roughness Ra is calculated. The substrate surface roughness was calculated by averaging the measured values of the obtained 10 surfaces × 10 points = total 100 points. The lower the value, the higher the performance.

(7) Scratch point Using both Candela 5100 optical surface analyzer as a measurement object, measure the scratch point by using a Candela 5100 optical surface analyzer on both surfaces of 5 substrates after polishing, that is, the total area of 10 surfaces. And it evaluated by the average value of the measured value of 10 surfaces. The lower the value, the higher the performance.

Example 1
(Preparation of extra-fine fiber assembly layer)
At room temperature (25 ° C.), N6 reagent was dissolved in a formic acid solvent at a concentration of 15 wt%. Using this as a spinning solution, by using an electrospinning method, a stainless steel nozzle having an inner diameter of 0.5 mm is used, and an electric field is applied at a voltage of 20 kV, and a stainless steel plate with conductive fluorine processing applied to the surface is attached to the drum. Spinning was performed at a spinning distance of 15 cm, and ultrafine fibers were accumulated to form an ultrafine fiber assembly layer. In the production of this ultrafine fiber assembly layer, the relative humidity of the spinning space was set to 30%.

The obtained ultrafine fibers made of N6 had an average fiber diameter of 0.13 μm, and had a mesh shape in which the ultrafine fibers overlapped in random directions. The basis weight of the ultrafine fiber assembly was 0.30 g / m ² .

(Preparation of fine fiber assembly layer)
Polystyrene with 22% copolymerization of N6 with sulfuric acid relative viscosity 2.63 as island component and 2-ethylhexyl acrylate as sea component (temperature 220 ° C., orifice size 2.0955 mmφ × 8 mm, melt index under load 2160 g is 15 g / 10 min) N6 and polystyrene are melted in a pressure melter at 275 ° C., respectively, and the number of islands is 200 islands / hole. Using a compound die, melt spinning at an island / sea weight ratio of 60/40 at a spinning speed of 1200 m / min, drawing, crimping and cutting 3.0 times in a liquid bath, a fineness of 4. A raw material cotton of 0 dtex sea-island type composite fiber was obtained.
Using this raw material of sea-island type composite fiber, a laminated web is formed through a card and cross wrapping process, and then punched at 1500 needles / cm ² at a needle depth of 8 mm using a needle punch machine in which a 1 barb needle is implanted. Needle punching was performed with the number of fibers to produce a composite fiber nonwoven fabric having a basis weight of 640 g / m ² and a density of 0.23 g / cm ³ . This non-woven fabric was subjected to hot water shrinkage at 95 ° C., and then 20 wt% of polyvinyl alcohol was added to the fiber weight, followed by drying. After dissolving and removing polystyrene, which is a sea component, with trichloroethylene, it was dried to a weight of 460 g. / M ² , a thickness of 1.70 mm, an apparent density of 0.27 g / cm ³ , and a fine fiber aggregate having a hardness of 45 ° were obtained. The average fiber diameter of the obtained fine fiber assembly layer was 1.2 μm.

(Production of polishing cloth)
Four ultrafine fiber aggregate layers are laminated on one fine fiber aggregate layer, and are heated and compressed using a flat roll in a wet state at a temperature of 120 ° C., a linear pressure of 10 kg / cm, and a processing speed of 2 m / min. Then, a polishing cloth having a basis weight of 495 g / m ² , a thickness of 1.40 mm, and an apparent density of 0.35 g / cm ³ was obtained.

(Polishing performance evaluation)
A polishing cloth was used as a tape having a width of 40 mm, and polishing was performed under the following conditions.
After a Ni-P plating treatment is applied to an aluminum substrate, a free abrasive slurry of colloidal silica having a primary particle diameter of 10 to 100 nm is dropped onto the surface of the polishing cloth using a disk that is polished and controlled to an average surface roughness of 0.2 nm. The polishing was performed for 30 seconds under the condition of the tape running speed of 5 cm / min. The polishing process was performed on both sides of each disk under the above conditions.

  The polished disc had a surface roughness of 0.12 nm, a scratch score of 10, a processed surface excellent in smoothness with no substantially concentric texture marks formed, and good workability. . Moreover, the substrate on which the magnetic layer was formed after the polishing process was extremely excellent in electromagnetic conversion characteristics.

(Example 2)
(Preparation of fine fiber assembly layer)
The fine fiber nonwoven fabric produced in Example 1 was impregnated with 12% DMF solution of polyurethane (polyester of polymer diol: polyether ratio: 75:25), squeezed with a nip roll, and solid with respect to the fiber weight. 25% by weight of polyurethane is applied per minute, the polyurethane is solidified with 30% DMF aqueous solution at a liquid temperature of 35 ° C., DMF is removed with hot water at about 85 ° C., and dried, resulting in a basis weight of 505 g / m ² , thickness A fine fiber aggregate having a density of 1.50 mm, an apparent density of 0.34 g / cm ³ , and a hardness of 40 ° was obtained.

(Production of polishing cloth)
Four ultrafine fiber aggregate layers produced in Example 1 are laminated on one fine fiber aggregate layer, and overheated compression is performed under the same conditions as in Example 1, with a basis weight of 530 g / m ² and a thickness. A polishing cloth having a diameter of 1.44 mm and an apparent density of 0.37 g / cm ³ was obtained.

(Polishing performance evaluation)
The polishing cloth was made into a tape having a width of 40 mm, and polishing was performed under the same conditions as in Example 1. The polished disk had a surface roughness of 0.10 nm, a scratch score of 5, a processed surface with excellent smoothness with no substantially concentric texture marks formed, and good workability. . By impregnating the fine fiber structure with polyurethane, the cushioning property was improved and the performance was improved. Moreover, the substrate on which the magnetic layer was formed after the polishing process was extremely excellent in electromagnetic conversion characteristics.

(Example 3)
(Production of polishing cloth)
On the ester polyurethane (Misumi Co., Ltd. “MUR-200”) (hardness 40 °), 6 ultrafine fiber assembly layers prepared in Example 1 were coated with an acrylic adhesive to a thickness of 30 μm. Then, they were bonded together and heated and compressed with the flat roll used in Example 1 to obtain an abrasive cloth.

(Polishing performance evaluation)
The polishing cloth was made into a tape having a width of 40 mm, and polishing was performed under the same conditions as in Example 1. The disk after polishing had a surface roughness of 0.15 nm, a scratch score of 19, a processed surface excellent in smoothness with no substantially concentric texture marks formed, and good workability. . Moreover, the substrate on which the magnetic layer was formed after the polishing process was extremely excellent in electromagnetic conversion characteristics. Polishing performance improved by laminating a cushion layer.

Example 4
(Preparation of extra-fine fiber assembly layer)
At room temperature (25 ° C.), polyacrylonitrile having a number average molecular weight of 160,000 was dissolved in a dimethylformamide solvent at a concentration of 10 wt%. Using this as a spinning solution, an ultrafine fiber nonwoven fabric was produced in the same manner as in Example 1 by an electrostatic spinning method.

The fiber diameter of the obtained ultrafine fiber made of polyacrylonitrile was 0.14 μm on average, and it was a network in which the ultrafine fibers overlapped in random directions. The basis weight of the ultrafine fiber assembly was 0.30 g / m ² .

(Production of polishing cloth)
Four ultrafine fiber aggregate layers were laminated on one fine fiber aggregate layer produced in Example 2, and the basis weight was 533 g / min in the same manner as in Example 1 using a flat roll in a wet state. An abrasive cloth having m ² , thickness of 1.40 mm, and apparent density of 0.38 g / cm ³ was obtained.

(Polishing performance evaluation)
The polishing cloth was made into a tape having a width of 40 mm, and polishing was performed under the same conditions as in Example 1. The polished disc had a surface roughness of 0.10 nm, a scratch score of 6, a smooth processed surface on which substantially concentric texture marks were not formed, and good workability. . Moreover, the substrate on which the magnetic layer was formed after the polishing process was extremely excellent in electromagnetic conversion characteristics.

(Comparative Example 1)
(Production of polishing cloth)
Using the fine fiber assembly layer produced in Example 2 and half-cutting in the thickness direction, the napped surface is subjected to three-stage buffing on the non-sliced surface using an endless sandpaper with a sandpaper count of 240 To form a napped sheet-like material. The napped sheet was used as an abrasive cloth, and an abrasive cloth having a thickness of 0.56 mm, a basis weight of 190 g / m ² , and an apparent density of 0.34 g / cm ³ was produced.

(Polishing performance evaluation)
Polishing performance was evaluated under the same conditions as in Example 1 except that the polishing cloth was a 40 mm wide tape. The polished disc has a surface roughness of 0.22 nm and a scratch score of 45, and is a processed surface with excellent smoothness, which has no problem in workability, but has texture marks that are substantially concentric. Met. The substrate on which the magnetic layer was formed after polishing was inferior in electromagnetic conversion characteristics.

(Comparative Example 2)
(Preparation of fine fiber assembly layer)
Using PET with sulfuric acid relative viscosity 0.716, melted in a pressure melter at 295 ° C, melt spun at a die temperature of 295 ° C at a spinning speed of 1200 m / min, and then stretched 3.0 times in a liquid bath The raw cotton was obtained through crimping and cutting.

Using this raw cotton, a laminated web is formed through a card and cross wrapping process, and then needle punched at a punch number of 1500 / cm ² at a needle depth of 8 mm with a needle punch machine in which a needle of 1 barb is implanted. , Impregnated with 13% DMF solution of polyurethane (polyester of polymer diol: polyether ratio: 75:25), squeezed with a nip roll to give 30% by weight of polyurethane with solid content to fiber weight, Polyurethane is solidified with a 30% DMF aqueous solution at a liquid temperature of 35 ° C., DMF is removed with hot water at about 85 ° C., compressed in the thickness direction, and dried to have a basis weight of 590 g / m ² , a thickness of 1.64 mm, and a density of 0 A fine fiber aggregate having a hardness of .36 g / cm ³ and a hardness of 47 ° was produced. The average fiber diameter of the obtained fine fiber assembly layer was 13.6 μm.

(Production of polishing cloth)
Four ultrafine fiber aggregate layers prepared in Example 1 are laminated on one fine fiber aggregate layer, and overheated compression is performed under the same conditions as in Example 1, with a basis weight of 600 g / m ² and a thickness. A polishing cloth having a diameter of 1.61 mm and an apparent density of 0.37 g / cm ³ was obtained.

(Polishing performance evaluation)
Polishing performance was evaluated under the same conditions as in Example 1 except that the polishing cloth was a 40 mm wide tape. The polished disk had a surface roughness of 0.25 nm and a scratch score of 94. Since a fiber structure having a fiber diameter of 10 μm or more was laminated, a part of 13.6 μm fibers was exposed to the surface during polishing and contributed to the polishing, so that the pressing pressure of the abrasive grains became too high and many scratch defects occurred. In addition, the substrate on which the magnetic layer was formed after polishing was inferior in electromagnetic conversion characteristics.

(Comparative Example 3)
(Production of polishing cloth)
On the ester-based polyurethane ("MUR-200" manufactured by MISUMI Corporation) (hardness 70 °), the 6 ultrafine fiber assembly layers prepared in Example 1 were applied so that the acrylic pressure-sensitive adhesive had a thickness of 30 µm. Then, they were bonded together and heated and compressed with the flat roll used in Example 1 to obtain an abrasive cloth.

(Polishing performance evaluation)
Polishing performance was evaluated under the same conditions as in Example 1 except that the polishing cloth was a 40 mm wide tape. The disc after polishing had a surface roughness of 0.28 nm and a scratch score of 86. By laminating with a polymer elastic body layer having high hardness, the pressing pressure becomes too high, resulting in high surface roughness and many scratch defects. In addition, the substrate on which the magnetic layer was formed after polishing was inferior in electromagnetic conversion characteristics.

Claims (6)

  From an ultrafine fiber structure having an average fiber diameter of 1.0 nm to 1.0 μm and a composite fiber structure in which fine fiber structures having an average fiber diameter of 0.50 to 10 μm are laminated manufactured by an electrostatic spinning method A polishing cloth characterized by comprising:   A polishing cloth comprising an ultrafine fiber structure having an average fiber diameter of 1.0 nm to 1.0 μm and a composite structure obtained by laminating a polymer elastic body layer, which is produced by an electrostatic spinning method.   The abrasive cloth according to claim 1, wherein the composite fiber structure includes a polymer elastic body.   The abrasive cloth according to claim 2 or 3, wherein the polymer elastic body is polyurethane.   The polishing according to any one of claims 2 to 4, wherein the surface of the fine fiber structure and the elastic polymer body has a hardness measured according to JIS K-6253A of 30 to 60 °. cloth.   The polishing cloth according to any one of claims 1 to 5, wherein a reinforcing layer is laminated on one side.