JP4457758B2 - Washed cloth - Google Patents

Description

The present invention relates to a cleaning cloth for cleaning the surface of a magnetic recording medium substrate, and more particularly to a cleaning cloth for efficiently cleaning the surface of a magnetic recording medium substrate after texturing. .

As the recording density of magnetic recording media increases, the size of 1 bit, which is the minimum unit of data written to the magnetic recording media, is becoming increasingly smaller. As the bit size is reduced, the deterioration of electromagnetic conversion characteristics such that Resolution (the ratio of HF output to LF output) is low and SNR (ratio of noise to signal) is also reduced. As a substrate for a magnetic recording medium, an aluminum-based substrate is subjected to texture processing for forming fine grooves in the circumferential direction of the substrate surface after the substrate surface is subjected to a non-magnetic plating process such as Ni-P plating. The electromagnetic conversion characteristics are not at a sufficiently satisfactory level. On the other hand, in the magnetic recording medium using a glass-based substrate, an isotropic medium has been mainstream, but electromagnetic conversion characteristics are lower than that of an anisotropic medium of an aluminum-based substrate. In order to obtain the same characteristics as an anisotropic medium in an isotropic medium, it is necessary to increase the magnetization in the circumferential direction, so that the thickness of the magnetic layer increases, and as a result, the medium noise caused by the magnetic film is reduced. Increased results. Therefore, it is necessary to efficiently produce an anisotropic medium on a glass substrate, and recently, a method of producing an anisotropic medium of a glass substrate by directly texturing the surface of the glass substrate has been proposed. It was.

Conventionally, when manufacturing a substrate for a magnetic recording medium, both an aluminum-based substrate and a glass-based substrate are polished to be composed of organic matter or fine dust adhering to the substrate surface during texturing, diamond remaining on the substrate surface, etc. after texturing. In order to remove processing residues such as small pieces of abrasive grains, polishing scraps and slurry liquid, scrub cleaning of cup type or roll type, immersion cleaning with chemical liquid or ultrasonic using dip layer, etc. are performed, then dried The film is subjected to a film forming process of an underlayer, a magnetic layer, and a protective layer.
However, in order to cope with the recent increase in recording density of magnetic recording media, the density of textured grooves on the substrate surface formed by texturing is high, the roughness is reduced, and it is becoming increasingly finer. Processing residues such as small pieces of abrasive grains, polishing debris and slurry liquid remaining in the groove cannot be removed, and in the case of a magnetic recording medium, problems such as magnetic defects and error defects due to these residues occur. However, there is a problem that the performance of the magnetic recording medium is reduced. On the other hand, among conventional cleaning methods, a method (Patent Document 1) for efficiently cleaning using a scrub made of polyvinyl acetal resin has been proposed, but organic substances adhering to the substrate surface are removed. However, the removal of small pieces of abrasive grains, polishing scraps, and slurry residues was insufficient.
In addition, a method in which an aqueous solution of an organic acid detergent is permeated into a woven fabric obtained by spinning ultrafine fibers having a diameter of 10 μm or less or a raised fabric obtained by raising the woven fabric, and is brought into contact with the substrate surface for cleaning (Patent Document 2). In this method, although the removal effect is improved by removing the foreign matter from the surface by the cleaning liquid and scraping out the foreign matter by the ultrafine fibers, compared to scrub cleaning and immersion cleaning, it is derived from the woven tissue of the woven fabric. Since the surface irregularities exist and the smoothness is inferior, the portions where the ultrafine fibers are not sufficiently scraped are scattered, and as a result, the magnetic defects and error defects cannot be sufficiently suppressed.

Therefore, there is a demand for a cleaning cloth that can efficiently scrape out foreign matters remaining in a texture groove that is formed by texturing and that is refined with high accuracy.
Japanese Patent Laid-Open No. 10-49868 JP 2003-178432 A

  The present invention solves the above-mentioned problems, and removes processing residues such as small pieces of polishing abrasive grains, polishing scraps and slurry liquid remaining in textured grooves of a magnetic recording medium substrate that has been refined with high precision and formed by texturing. The present invention provides a cleaning cloth that can be scraped and removed efficiently.

  In order to solve the above problems, the present invention has the following configuration.

That is, the cleaning cloth of the present invention is
On at least one surface of the nonwoven fabric following ultrafine fibers having an average fiber diameter 5μm is formed by entangled, we have a napped of ultrafine fibers, met cleaning work cloth for cleaning the magnetic recording medium substrate surface subjected to texturing The cleaning cloth is characterized in that the linear density of the number of surface fibers on the surface having the napping is 30/100 μm width or more .
In the method for cleaning a surface of a magnetic recording medium substrate according to the present invention, the cleaning cloth is infiltrated with an aqueous solution of water and / or an organic acid cleaning agent, and the cleaning cloth is brought into contact with the surface of the magnetic recording medium substrate. And cleaning the surface of the magnetic recording medium substrate.

  According to the present invention, since it has a uniform and fine substrate surface and is excellent in surface smoothness, it has excellent fit to a texture groove formed by texturing and highly refined, and a texture groove. Scattering and removal of foreign matter remaining on the substrate is extremely high, and the defect rate of the magnetic recording medium substrate can be suppressed.

It is important that the average fiber diameter of the ultrafine fibers contained in the nonwoven fabric constituting the washed cloth of the present invention is 5 μm or less. When the average fiber diameter exceeds 5 μm, the fit to fine irregularities on the surface of the substrate formed after texturing is inferior, the foreign matter is not scraped out sufficiently, and the cleaning efficiency is lowered. In addition, from the viewpoint of achieving both fit to fine irregularities on the substrate surface, pressing force of the fibers on the substrate surface, and scraping force, the average fiber diameter is preferably in the range of 0.1 to 5 μm, 0.5 More preferably, it is in the range of ˜2 μm. The average fiber diameter here is obtained by observing a cross section cut in the thickness direction of the nonwoven fabric with a scanning electron microscope (SEM), measuring the fiber diameters of arbitrary 100 ultrafine fibers, and calculating the average value. It is what

  The means for obtaining ultrafine fibers is not particularly limited, but it is preferable to use ultrafine fiber generating fibers. As ultra-fine fiber generation type 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. Adopting peelable composite fibers, multilayer composite fibers, etc. that split fibers into ultrafine fibers by arranging fibers and two-component thermoplastic resin alternately in a fiber cross section radially or in layers and separating and separating each component Can do. Above all, the sea-island type composite fiber can buff a nonwoven fabric containing ultrafine fibers because it can provide an appropriate gap between the island components, that is, between the ultrafine fibers inside the fiber bundle, by removing the sea components. Thus, it is preferable because the nap-opening property is excellent when the napped surface is formed, and the ultrafine single fiber can be brought into uniform contact with the substrate surface and the removal efficiency can be improved.

  The method for obtaining the sea-island type composite fiber is not particularly limited. For example, (1) a method of blending and spinning two or more polymers in a chip state, and (2) kneading a polymer of two or more components in advance to form a chip. (3) A method of mixing and spinning two or more polymers in a melted state in a spinning machine pack with a static kneader or the like, and (4) a sea-island type composite such as Japanese Patent Publication No. 44-18369. Examples include a polymer mutual array system in which two components of sea islands are mutually aligned and spun using a base. In the present invention, polymer selection is easy, the dispersibility of ultrafine fibers is excellent, and ultrafine fibers having a uniform fiber diameter can be stably obtained. Sea-island type composite fibers are preferred.

  In particular, regarding the uniformity of the fiber diameter, the fiber diameter CV value of the ultrafine fiber is preferably 10% or less. The fiber diameter CV value here refers to a value obtained by measuring the fiber diameter of any 100 ultrafine fibers, calculating an average value and a standard deviation, and expressing a value obtained by dividing the standard deviation by the average value as a percentage (%). The smaller the value is, the more uniform it is. By setting the fiber diameter CV value to 10% or less, the pressing force and scraping force of the ultrafine fibers on the napped surface to the substrate surface become uniform over the entire substrate surface, and the cleaning efficiency can be improved.

  The cross-sectional shape of the island fiber obtained by removing the sea-island type composite fiber and the sea component is not particularly limited. For example, a polygon such as a circle, an ellipse, a flat, a triangle, a fan, a cross, Y, H, X, W, Examples thereof include C and π-type. Also, the number of polymer species to be used is not particularly limited, but it is preferably 2 to 3 components in consideration of spinning stability, and particularly composed of 2 components of sea 1 component and island 1 component. preferable. In addition, the component ratio at this time is preferably 0.2 to 0.9 by weight ratio of island fibers to sea-island type composite fibers, and more preferably 0.3 to 0.8. If it is less than 0.2, the removal rate of sea components is large, the productivity is remarkably lowered, and this is not preferable in terms of cost. On the other hand, if it exceeds 0.8, the spreadability of the island fibers is inferior, a uniform raised surface cannot be obtained, and the cleaning efficiency is lowered, which is not preferable.

Examples of the resin constituting the sea-island type composite fiber include a combination of two or more kinds of resins capable of generating ultrafine fibers. For example, polyamides such as nylon 6, nylon 66, nylon 12, copolymer nylon, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyesters such as copolymer polyester, polyethylene, polypropylene, polymethylpentene, polystyrene, Examples of synthetic resins that can be used include polyolefins such as polymerized polystyrene, fatty acid polyester polymers such as polylactic acid, lactic acid copolymer, and polyglycolic acid, and fatty acid polyesteramide polymers.
As the ultrafine fiber component (island component) of the sea-island composite fiber, polyamides and polyesters are preferably used from the viewpoint of excellent hydrophilicity and wear resistance. In particular, nylon 6, nylon 66, nylon 12, copolymer nylon polyamides, polytrimethylene terephthalate, and copolymerized polytrimethylene terephthalate polyesters are water and / or aqueous solutions of organic acid detergents used for substrate cleaning. It has excellent compatibility with the substrate, is flexible, and has an excellent fit to fine irregularities on the substrate surface, so that the processing residue such as small pieces of abrasive grains remaining on the substrate surface is scraped and removed while holding the processing residue on the ultrafine fiber Is high and is preferably used.

  On the other hand, as the sea component of the sea-island type composite fiber, polyethylene, polypropylene, polystyrene, copolymer polystyrene, sodium sulfoisophthalic acid are used because they have chemical properties that are more soluble and decomposable than the polymer that constitutes the island component. It is preferable to use a copolymerized polyester, polylactic acid, or the like having a copolymerization component such as polyethylene glycol. As a solvent for dissolving sea components, an organic solvent such as toluene and trichloroethylene is used in the case of polyethylene, polypropylene, polystyrene, and copolymer polystyrene, and an alkaline aqueous solution such as sodium hydroxide is used in the case of copolymer polyester and polylactic acid. The sea component can be removed by immersing the sea-island type composite fiber in a solvent and performing a stenosis.

  An example of the method for producing the washed cloth of the present invention is to spin a composite fiber capable of generating ultrafine fibers having an average fiber diameter of 5 μm or less, and obtain raw cotton through drawing, crimping and cutting. Using the raw cotton made of this ultrafine fiber-generating fiber, an entanglement process such as needle punching is performed to form a nonwoven fabric. Next, one component of the composite fiber (for example, the sea component of the composite fiber having a sea-island structure) is dissolved and removed or separated by physical and chemical action to form ultrafine fibers. Next, at least one surface of the obtained sheet is buffed to form a raised surface. In this process, before or after forming ultrafine fibers, applying a polymer elastic body in the sheet, applying a high-speed fluid flow treatment such as water jet punching, applying a stagnation treatment, laminating a film on one side May be combined and adopted as appropriate.

In order to obtain a sea-island type composite fiber nonwoven fabric, it is preferable to perform needle punching after forming a laminated web in which the sea-island type composite fiber is shortened and arranged in the sheet width direction using a card cross wrapper. . In terms of forming a web, a random web or the like can also be used. Long fiber nonwoven fabrics formed directly from spinning, such as melt blow and spun bond, may be used, but short fiber nonwoven fabrics are excellent in entanglement between ultrafine fibers and denseness of surface fibers, and the density of surface fibers is small and uneven density is small. This is particularly preferable because of its good cleaning efficiency.
The number of punches in the needle punching process is preferably 1000 to 4000 / cm ² from the viewpoint of forming a dense raised surface by high entanglement of fibers. If the density is less than 1000 fibers / cm ² , the surface fibers are inferior in density, leading to a decrease in cleaning efficiency. If exceeding 4000 fibers / cm ² , workability is deteriorated and fiber damage is large, leading to a decrease in strength. It is not preferable. The fiber density of the composite fiber nonwoven fabric sheet after needle punching is preferably 0.2 g / cm ³ or more from the viewpoint of densification of the number of surface fibers.

  From the viewpoint of densification of the number of surface fibers, the composite fiber nonwoven fabric thus obtained is preferably shrunk by dry heat or wet heat, or both, and further densified.

  In addition, after the ultrafine fiber treatment, the interlacedness between the ultrafine fiber and the ultrafine fiber, the ultrafine fiber and the ultrafine fiber bundle, or the ultrafine fiber bundle and the ultrafine fiber bundle is further increased and densified, and the ultrafine fiber bundle is opened. High speed fluid flow treatment such as water jet punching treatment and stagnation treatment using liquid flow dyeing machine, Wins dyeing machine, zigger dyeing machine, tumbler, relaxer, etc., as appropriate from the viewpoint of improving fineness and smoothness. You may carry out in combination. In the case where the high-speed fluid flow treatment and the stagnation treatment are performed in combination, it is preferable to perform the stagnation treatment after the high-speed fluid flow treatment is performed from the viewpoint of suppressing dimensional variation during the stagnation processing. As the high-speed fluid flow treatment, a water jet punching treatment using a water flow is preferable from the viewpoint of the working environment. When the water jet punching treatment is performed, the water is preferably carried out in a columnar flow state. In order to obtain a columnar flow, generally, a method of ejecting from a nozzle having a diameter of 0.06 to 1.0 mm at a pressure of 1 to 60 MPa is suitably used.

  In the cleaning cloth of the present invention, the pressing force of the ultrafine fibers on the surface of the substrate having fine irregularities, the cushion for controlling the fit and the role of maintaining the fiber shape are imparted, and the fine remaining on the substrate surface For the purpose of increasing the cleaning efficiency of foreign substances, it is preferable that a polymer elastic body is contained inside the nonwoven fabric of ultrafine fibers. As such a polymer elastic body, an elastomer resin such as polyurethane, acrylic resin, polyester, polyamide or polyolefin, ethylene-vinyl acetate resin, or the like can be used. Among these, polyurethane is preferable from the viewpoint of processability and cushioning properties in the process of the present invention. For example, when it is a polyurethane-based synthetic resin, the molecular weight of the polymer diol component of the polyurethane is preferably 500 to 5000, more preferably 1000 to 3000, and the diol component that is the raw material is a polyether diol. Polyester diol, polycarbonate diol, polylactone diol or a copolymer thereof is preferably used. Moreover, as a diisocyanate component, aromatic diisocyanate, alicyclic isocyanate, aliphatic isocyanate, etc. can be used.

  As a method for applying such polyurethane, a method of solidifying after applying or impregnating polyurethane can be employed. Among these, from the viewpoint of processability, a method of wet coagulation after impregnating a polyurethane solution into a sheet of ultrafine fiber nonwoven fabric is preferably used.

  The weight average molecular weight of the polyurethane is preferably 100,000 to 300,000, more preferably 150,000 to 250,000. By setting the weight average molecular weight to 100,000 or more, it is possible to maintain the strength of the obtained sheet and to prevent the fine fibers on the napped surface 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.

  Moreover, it is preferable that the gelation point of a polyurethane is 2.5-6.0 ml from the viewpoint of satisfying the denseness and uniformity of the ultrafine fibers on the raised surface when the buffing treatment is performed. More preferably, it is the range of 3-5 ml. The gelation point of polyurethane refers to 100 g of N, N′-dimethylformamide (hereinafter abbreviated as DMF) solution of 1% by weight of polyurethane while stirring distilled water dropwise into this solution at a temperature of 25 ± 1 ° C. This is the value of the amount of water dripping when polyurethane solidifies under the conditions and becomes slightly cloudy. For this reason, it is necessary to use the DMF used for the measurement having a water content of 0.03% or less. The measurement method described above is described on the assumption that the polyurethane DMF solution is transparent. However, when the polyurethane DMF solution is slightly cloudy in advance, the solidification of the polyurethane starts and the degree of cloudiness changes. The amount of water dropped can be regarded as the gel point. When the gel point is less than 2.5 ml, the solidification rate is too high when the polyurethane is wet-coagulated, so that the polyurethane foam existing in the nonwoven fabric is greatly rough, and some of the foaming is poor. As a result, when the sheet surface is ground by buffing, the length of the napped fibers on the napped surface is uneven, and the area of the ultra fine fibers on the surface of the substrate becomes non-uniform and the foreign matter is scraped off. Since the places where the removal becomes insufficient are scattered, it is not preferable. On the other hand, if the gel point exceeds 6.0 ml, the solidification rate is too slow when the polyurethane is wet-coagulated, so that the polyurethane existing in the interior space of the nonwoven fabric has almost no foaming and is very thick. It exists as hard polyurethane, and when the surface of the nonwoven fabric sheet is ground by buffing treatment, it is difficult to grind polyurethane, the length of raised fibers of the ultrafine fibers on the raised surface is very short, and the fiber bundle is not very open. In addition, the uneven density of the surface fiber density increases, which is not preferable because the scraping efficiency of the foreign matter remaining on the substrate surface is significantly reduced.

  In the washed cloth of the present invention, in order to achieve both the denseness and uniformity of the surface fiber distribution, that is, the state in which the fiber bundles constituting the napped fibers are excellent in opening, the polyurethane has a fiber bundle of ultrafine fibers. The entangled nonwoven fabric is preferably not substantially present inside the fiber bundle of ultrafine fibers. As a method of obtaining a form that does not substantially exist inside the fiber bundle of ultrafine fibers, polyurethane is made into a solution with a solvent such as dimethylformamide, and (1) a nonwoven fabric in which ultrafine fiber-generating sea-island composite fibers are entangled, A method of impregnating the polyurethane solution and coagulating it in water or an organic solvent aqueous solution, and then dissolving and removing the sea component of the sea-island composite fiber with a solvent that does not dissolve polyurethane; (2) a sea-island composite of ultrafine fiber generation type Polyvinyl alcohol having a saponification degree of preferably 80% or more is imparted to the nonwoven fabric in which the fibers are entangled, and after protecting most of the periphery of the fibers, the solution of the sea-island type composite fibers is impregnated in water or an aqueous organic solvent For example, a method of removing polyvinyl alcohol after coagulation with sol can be preferably used.

  In the cleaning fabric of the present invention, cushioning and fitting properties are important in terms of cleaning accuracy, and are controlled and adjusted by the ratio of fine fibers and polymer elastic bodies and the porosity (which can be seen by the apparent density). The content of the polymer elastic body is preferably 0.5 to 50% with respect to the total weight of the sheet, and the surface state, porosity, cushioning properties, hardness, strength, etc. of the washed cloth are appropriately adjusted depending on the content. can do. If it is less than 0.5%, it is not preferable because many fibers fall off and the cleaning efficiency is lowered. If it exceeds 50%, the processability and productivity are inferior, the polymer elastic body is easily exposed on the sheet surface, and the portions where the foreign matter remaining on the substrate surface is not sufficiently scraped off are scattered, which is not preferable.

  It is important that the washed cloth of the present invention has napped fibers of at least one surface of a non-woven fabric containing ultrafine fibers. Although this napping is generally obtained by buffing treatment, the buffing treatment herein is preferably performed by a method of grinding the sheet surface of the ultrafine fiber nonwoven fabric using a sandpaper or a roll sander. In particular, by raising the sheet surface using sandpaper, uniform and dense napping can be formed. Furthermore, in order to improve the fit to the substrate surface and improve the cleaning efficiency, in order to improve the uniformity and denseness of the fiber distribution on the surface of the ultrafine fiber nonwoven fabric sheet and to reduce the direction of napped fibers extremely It is preferable to reduce the grinding load. When the grinding load is high, there are many napped fibers that are curly, and the napped fibers tend to stick together in a bundle, so that ultrafine fibers are pressed against the substrate surface and scraped off, and cannot be removed. This is not preferable because the remaining portions of water are scattered. In order to reduce the grinding load, it is preferable to appropriately adjust the number of buff stages, sandpaper count, and the like. Among these, it is more preferable that the number of buff stages is multistage buffing having 3 or more stages, and the sandpaper used for each stage is in the range of 150 to 600 in the JIS standard.

  In the cleaning cloth of the present invention, it is preferable that the linear density of the number of surface fibers on the surface having napping is 30/100 μm or more. The linear density of the number of surface fibers here is defined as follows. Using the raised surface of the washed cloth as an observation surface, observation is performed with a scanning electron microscope (hereinafter abbreviated as SEM), and 30 points of 100 μm width are extracted at intervals of 1 mm in the continuous longitudinal direction of the nonwoven fabric sheet. The number of ultrafine fibers present in the outermost layer at each extraction location is measured, and the average value is calculated. Let the obtained value be the linear density of the number of surface fibers. When the linear density of the number of surface fibers is less than 30/100 μm width, the density of the surface fibers is inferior, and the removal efficiency of foreign matters remaining on the substrate surface is lowered, which is not preferable.

Furthermore, the apparent density of the cleaning cloth of the present invention is 0.2 to 0.8 g / cm ³ considering the denseness of the surface fibers, the smoothness of the sheet surface, the cushioning property, and the fit to the substrate surface. It is preferable that it exists in the range, and it is more preferable that it is 0.3-0.7 g / cm < ³ >.

  When the substrate surface is cleaned with the cleaning cloth of the present invention, if the dimensional change occurs, the substrate surface cannot be cleaned uniformly. Therefore, in order to give form stability to the cleaning cloth, a reinforcing layer is provided on one side. Are preferably adhered. In addition, when providing a reinforcement layer, it is made for the opposite surface of the nonwoven fabric sheet which adhere | attached the reinforcement layer to become a napped surface.

As a method of adhering the reinforcing layer, any of a thermocompression bonding method, a frame lamination method, and a method of providing an adhesive layer between the reinforcing layer and the nonwoven fabric sheet layer may be adopted. Any adhesive layer can be used as long as it has rubber elasticity such as polyurethane, SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), polyamino acid, acrylic adhesive, etc., but cost and practicality are considered. Adhesives such as NBR and SBR are preferred. As an application method, it is applied to a nonwoven fabric sheet in the form of emulsion or latex.
As the reinforcing layer, a woven or knitted fabric, a nonwoven fabric using heat-bonding fibers, or the like may be used. However, in order to perform high-precision cleaning, it is preferable to use a film-like material that is uniform in thickness and physical characteristics. When woven or knitted fabric or heat-bonded fibers are used for the reinforcing layer, the unevenness of the surface of the reinforcing layer is too large, and the unevenness of the reinforcing layer may be reflected on the entire cleaning cloth. This may impair the fit of the cleaning and may lead to a reduction in cleaning efficiency. On the other hand, since the film-like product is excellent in surface smoothness, high-precision cleaning can be performed without impairing the smoothness of the surface of the cleaning cloth. Any material having a film shape such as polyolefin, polyester, or polyphenyl sulfide can be used as the material for the film here, but it is preferable to use a polyester film in view of versatility. When providing a reinforcing layer made of a film, it is possible to balance the thickness with the sheet layer made of nonwoven fabric from the viewpoint of satisfying all of the form stability, cushioning properties, and fitability to the substrate surface during cleaning processing. The sheet layer made of nonwoven fabric is necessary, and the finished thickness is preferably 0.4 mm or more, and the thickness of the film is preferably 20 to 100 μm. If the thickness of the sheet layer made of non-woven fabric is less than 0.4 mm, the dimensional change during the cleaning process is large and uniform cleaning is not possible, so a reinforcing layer is necessary, but the effect of the reinforcing layer is strong and the cushioning property is lost. End up. If the thickness of the film layer is less than 20 μm, it is difficult to suppress the dimensional change during the cleaning process, and if it exceeds 100 μm, the rigidity of the entire cleaning cloth becomes too high, so that the fit to the substrate is impaired. This is not preferable because uniform cleaning cannot be achieved.

  The method of performing the cleaning process using the cleaning cloth of the present invention is used as a tape obtained by cutting the cleaning cloth into a tape shape having a width of 30 to 50 mm from the viewpoint of processing efficiency and stability. Next, while the substrate is continuously rotated, the cleaning cloth in a tape shape is pressed against the textured substrate while the cleaning cloth or the substrate is reciprocated in the radial direction of the substrate to continuously clean the cleaning cloth. Let it run. At that time, it is a preferable method to supply the surface of the cleaning cloth with water and / or an aqueous solution of an organic acid cleaning agent and clean the surface of the substrate with ultrafine fibers on the surface.

  The organic acid detergent used here preferably contains at least one of sulfonic acid, citric acid, malic acid, or acetic acid.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely using an Example, this invention is not limited only to a following example. Moreover, the evaluation methods and measurement conditions used in Examples and Comparative Examples will be described below.
(1) Average fiber diameter and fiber diameter CV value Observe with a scanning electron microscope (SEM) using the cross section of the washed cloth cut in the thickness direction as an observation surface, and measure the fiber diameter of any 100 ultrafine fibers, A standard deviation and an average value are calculated using this as a population. This average value was taken as the average fiber diameter, and the value obtained by dividing the standard deviation by the average value as a percentage (%) was taken as the fiber diameter CV value.
(2) The linear density and the linear density CV value of the number of surface fibers Using the raised surface of the washed cloth as the observation surface, the surface is observed with a scanning electron microscope (SEM), and is 100 μm wide at intervals of 1 mm in the sheet continuous longitudinal direction. Extract 30 locations. The number of ultrafine fibers present in the outermost layer at each extraction location is measured, and the average value is calculated. The obtained value was defined as the linear density of the number of surface fibers.
(3) Defect disk occurrence rate In the cleaning process test, 100 disk substrates are set as one set, and a total of three sets are performed. For each set, the occurrence rate of defective disks due to foreign matters remaining on the substrate surface, such as magnetic defects and error defects, was calculated, and the average value of the occurrence rates in the three sets was defined as the defective disk occurrence rate. When the defective disk occurrence rate is less than 5%, the workability is good, and when it exceeds 5%, the workability is bad.

Example 1
Using nylon 6 as the island component and copolymer polystyrene as the sea component, melt spinning is performed at an island / sea weight ratio of 40/60 through a sea-island type compound base of a polymer inter-array system with 100 islands / hole. After stretching at a draw ratio of 3 times, crimped and cut, a sea-island-type composite fiber having a composite fineness of 4 dtex was formed. Next, using this raw cotton, a laminated web was obtained through a card and a cross wrapper, and needle punched with a punch number of 2000 / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a density of 0.2 g / cm ³ .
The nonwoven fabric was shrunk in hot water at 85 ° C. and then impregnated with a 10% aqueous solution of polyvinyl alcohol and dried. Thereafter, the copolymer polystyrene, which is a sea component, was dissolved and removed in trichlorethylene and dried to obtain an ultrafine fiber nonwoven fabric.
Next, 25% by weight of polyurethane (with a polymer diol having a ratio of polyether to polyester of 75:25 and a gel point of 3.5 ml) based on the total weight of the sheet is impregnated in water. After the polyurethane was coagulated, polyvinyl alcohol was dissolved and removed with hot water.

Thereafter, the surface of the sheet was buffed in three steps with sand paper of JIS regulation 240th to obtain a washed cloth having a thickness of 0.45 mm, a basis weight of 150 g / m ² and an apparent density of 0.33 g / cm ³ . The average fiber diameter of the ultrafine fibers in the washed cloth was 1.4 μm, and the linear density of the number of surface fibers was 40/100 μm width.

This cleaning cloth was used as a tape having a width of 40 mm, and cleaning was performed under the following conditions.
Using a slurry containing diamond abrasive grains having an average particle diameter of 0.1 μm and napped sheets made of polyethylene terephthalate fibers having an average fiber diameter of 2 μm, the glass substrate surface mirror-finished by polishing is textured for 10 seconds. gave. The textured substrate surface had an average surface roughness of 2.5 × 10 ⁻¹⁰ m (angstrom) and a line density of 12 lines / μm width. A tape made of a cleaning cloth is applied to the obtained textured substrate surface with a processing tension of 20 N applied, and the tape is run at a speed of 5 cm / min. Washing was performed for 20 seconds while dropping an aqueous solution containing. This operation was performed for a total of three sets, with one set of 100 discs. As a result of evaluating the defective disk occurrence rate of the obtained disk, it was 2% and the workability was good.

Example 2
An adhesive mainly composed of NBR was applied to the back surface of the cleaning cloth obtained in Example 1, and a 50 μm thick polyester film was pressure-bonded to prepare a cleaning cloth. Using this washed cloth, washing was performed in the same manner as in Example 1. As a result of evaluating the defective disk occurrence rate of the obtained disk, it was 1.3%, and the workability was very good.

Comparative Example 1
Sea island type fiber (sea component: copolymerized polyethylene terephthalate of terephthalic acid and 5-sodium sulfoisophthalic acid, island component: polyethylene terephthalate, number of islands: 70 islands, island / sea weight ratio: 80/20) 56 dtex, A 9-filament raw yarn was used to weave into a plain weave. Subsequently, the sea component of the sea-island fiber was dissolved and removed in an alkaline aqueous solution. Then, it heat-set on the conditions of 180 degreeC with the pin tenter, and finished into the plain fabric of warp density 170 piece / inch and weft density 130 piece / inch.

  The average fiber diameter of the ultrafine fibers constituting the warp and the weft was 3 μm, and the linear density of the number of surface fibers was 15/100 μm width.

  This plain woven fabric was used as a washed cloth, and washing was performed in the same manner as in Example 1. As a result of evaluating the defective disk occurrence rate with respect to the obtained disk, it was 12%, many of the disks in which a large number of residual foreign matters were detected, error defects occurred, and workability was poor.

Comparative Example 2
One side of the plain woven fabric obtained by the production method of Comparative Example 1 was subjected to a buffing treatment with sandpaper to obtain a brushed woven fabric. The average fiber diameter of the ultrafine fibers constituting the warp and the weft was 3 μm, and the linear density of the number of surface fibers was 17/100 μm width.

  This brushed fabric was used as a washed cloth, and washed by the same method as in Example 1. As a result of evaluating the defective disk occurrence rate with respect to the obtained disk, it was 10%, and many of the disks in which a large number of residual foreign matters were detected, error defects occurred, and workability was poor.

Claims (7)

On at least one surface of the nonwoven fabric following ultrafine fibers having an average fiber diameter 5μm is formed by entangled, we have a napped of ultrafine fibers, met cleaning work cloth for cleaning the magnetic recording medium substrate surface subjected to texturing The cleaning cloth is characterized in that the linear density of the number of surface fibers on the surface having the napping is 30/100 μm width or more . 2. The cleaning cloth according to claim 1, wherein the fiber diameter CV value of the ultrafine fiber is 10% or less. The cleaning cloth according to claim 1 or 2 , wherein the nonwoven fabric contains a polymer elastic body. 4. The washed cloth according to claim 3 , wherein the content of the polymer elastic body is 0.5 to 50% with respect to the total weight of the nonwoven fabric. The film according to any one of claims 1 to 4 , wherein a film is laminated on one surface of the nonwoven fabric. 6. The cleaning cloth according to claim 5, wherein the film has a thickness of 20 to 100 [mu] m. The cleaning work cloth according to any one of claims 1 to 6, an aqueous solution of water and / or organic acid based detergent impregnated, by washing in contact with the cleaning work cloth on the surface of the substrate for a magnetic recording medium A method for cleaning a surface of a magnetic recording medium substrate.