JP2011204353A - Wiping film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiping film in which neither scratch nor lint is generated on a surface to be treated, and which has a function to remove a foreign substance and surplus oil.SOLUTION: The wiping film has a flexible film-like base material and a wiping layer coated one surface of the base material where the wiping layer has a binder and fine particles formed of plastics dispersed therein.

Description

  The present invention relates to a material used for finishing a surface of a magnetic recording medium, and more particularly to a wiping film used for a cleaning process or a burnishing process of a magnetic disk surface.

  In recent years, with the development of information processing technology such as computers, magnetic recording media such as magnetic disks have been used as external storage devices.

A magnetic disk is generally subjected to a series of surface treatments such as lapping, polishing, and texturing on a non-magnetic substrate such as an aluminum alloy or glass to roughen the surface, and then the roughened non-magnetic substrate. A magnetic recording layer is formed on the magnetic substrate, and a protective film made of carbon, SiO ₂ or the like for protecting the magnetic recording layer is formed on the magnetic recording layer.

  After the formation of the protective film, film cleaning is performed in order to remove protrusions formed on the surface of the protective film and foreign matters on the surface of the magnetic disk. This film cleaning is generally performed using an abrasive film.

  Next, a fluorocarbon-based lubricant is applied on the protective film that has been cleaned to form a lubricating film, and deposits such as dust that adhere to the surface of the magnetic recording medium on which the lubricating film has been formed by burnishing Remove. This burnishing is also generally performed using an abrasive film. Thereafter, a predetermined test is performed to manufacture a magnetic recording medium conforming to the standard.

  Conventionally, as a polishing film used for film cleaning and burnishing, a wrapping film (precision abrasive) in which abrasive grains such as alumina particles and SiC particles are supported on a film made of polyethylene terephthalate or polyamide is used. For example, Japanese Patent Laid-Open Nos. 9-85628, 10-71572, and 11-114837 describe a wrapping film having such a configuration.

  In recent years, the technology for forming a protective film has been improved in order to increase the storage capacity of a magnetic disk, and a shift has been made from a sputtering method to a chemical vapor deposition (CVD) method. As a result, the characteristics of the film quality have changed, and the film thickness has become much finer and finer. In addition, the surface state of the magnetic disk after film formation has become more uniform and high in quality with high cleanliness (the number of abnormally grown protrusions and dust generated during formation has been reduced).

  To improve the quality of the formed film, the wrapping film used for film cleaning and burnishing also responds to this change. It has shifted to fine abrasive grains of 0.3 μm or less.

  However, since the wrapping film contains particles of hard inorganic material as an abrasive, there are defects that cause scratches on the surface of the magnetic disk if there are uneven projections on the surface of the wrapping film or if grain breakage occurs. There is. Further, if the abrasive grains remain on the disk surface, a fatal defect such as embedding of the abrasive grains in the disk may occur in the next process.

  Therefore, in recent years when the technology for forming the protective film has been improved, the tape for surface-treating the protective film of the magnetic disk is required to have a function of removing deposits by wiping without damaging rather than polishing the surface of the protective film. It has become so. Further, when burnishing is performed after the formation of the lubricating film, a surface structure having oil absorption characteristics is required in order to remove excess oil and make the lubricating film uniform.

  In other words, the required quality of the finishing material on the magnetic disk surface changes with the improvement of film quality and changes in the use process, and it is required to have a function capable of removing foreign matter and excess oil without generating scratches. It has been. In other words, the conventional emphasis on the polishing function is shifting to the emphasis on the foreign matter removal function (wiping function).

  Japanese Patent Application Laid-Open No. 5-66179 describes a cleaning film for treating the surface of a protective film of a magnetic recording medium. This cleaning film is composed of a woven fabric of ultrafine fibers, and is intended to be used for removing polishing debris after polishing with a wrapping film. Therefore, it does not contain abrasive grains per se and does not generate scratches on the surface of the magnetic disk.

  However, the ultrafine fiber is easily cut by tension or friction, and when it is cut, the fiber residue falls off from the woven fabric. Therefore, when this cleaning film is used instead of the wrapping film, there is a problem that the treated surface is contaminated with fiber residue. Therefore, a cleaning film composed of a woven fabric of ultrafine fibers has not been put into practical use as a material for treating the surface of the protective film of a magnetic recording medium.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a wiping film that has a function of removing foreign matter and excess oil without causing scratches or fiber debris on the surface to be treated. There is to do. At this time, particularly in the case of a wiping object such as a magnetic disk, in recent years, it has been required to change the surface roughness from nanobase to angstrom level, and the wiping film itself needs to cope with this.

  The present invention relates to a wiping film having a flexible film-like substrate and a wiping layer coated on one surface of the substrate, wherein the wiping layer includes a binder and plastic fine particles dispersed therein. A wiping film having the above object is achieved.

  The wiping film of the present invention contains no inorganic material particles or fiber material, and does not generate scratches or fiber debris on the surface to be treated. Further, the uneven surface has a non-uniform structure, and foreign matters and excess oil can be effectively removed from the surface to be treated.

  FIG. 1 is a cross-sectional view showing an example of the wiping film of the present invention. On the surface of the film substrate 1, plastic fine particles 2 are bonded with a binder resin 3 to form a layer 4 (hereinafter referred to as “wiping layer”). The use of the wiping film is to remove foreign matter and excess oil from the surface of the magnetic recording medium, mainly from the surface of the magnetic disk, and to make the lubricating film formed on the surface of the magnetic disk uniform.

Film-like substrate Film-like substrate is a polymer film that has enough strength to withstand tape cleaning and burnishing, strength to withstand coating and drying in the manufacturing process, heat resistance, little dimensional change, and flexibility Can be appropriately selected. A polymer film that has been conventionally used as a base material for a wrapping film is suitable.

  Examples of such polymer films include polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, polyolefin resins such as high density polyethylene and polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, Stretched or unmade of ethylene-vinyl alcohol copolymer, polyacrylonitrile, polyamide, acrylic acid ester, acrylic resin mainly composed of acrylic acid ester or methacrylic acid ester, polyacetal, cellulose triacetate, fiber derivative of cellulose diacetate, polycarbonate, etc. There is a stretched film.

  In particular, a biaxially stretched film of polyethylene terephthalate, nylon 6, or a polyimide film is preferable because it is excellent in coating suitability for the wiping layer, suitability for post-processing, and handling in actual equipment.

It is preferable that this film-like base material exhibits appropriate flexibility. For example, the flexural modulus is preferably 500 to 2000 kg / mm ² when measured based on JISK6911 using a sample having a thickness of 1 mm.

  The thickness of the film-like substrate is generally 5 to 125 μm, preferably 14 to 75 μm.

Plastic fine particles Conventionally, wrapping films that have been used for film cleaning and burnishing on the surface of magnetic recording media have used particles of inorganic material such as alumina as a component of the polishing layer. However, in order to prevent generation of scratches on the surface to be processed, the wiping film of the present invention uses fine particles made of plastic that are softer than the particles of the inorganic material. By combining such plastic fine particles and a binder, the surface of the wiping layer has a non-uniform rugged structure, and there is no scratch on the object to be polished, and there is provided an action to take in fine foreign matter and particles and an oil absorption action. .

  The plastic fine particles preferably have a Rockwell hardness of M10 to M130, particularly M85 to M105. This is because, if the Rockwell hardness of the plastic fine particles is less than M10, the plastic fine particles are flattened when the wiping film is used, and it becomes difficult to maintain the uneven structure on the surface. Thereby, the wiping effect cannot be obtained. If M130 is exceeded, scratches may occur on the surface to be processed.

  The shape of the plastic fine particles is not particularly limited, but is preferably spherical. This is because scratches are less likely to occur on the surface to be processed. As the size of the particles, those having an average particle diameter of 0.01 to 100 μm are preferable, and those having an average particle diameter of 0.1 to 10 μm are more preferable. If the average particle size of the particles is less than 0.0 lμm, the surface of the wiping layer of the film cannot be formed with irregularities having the surface roughness required for product design, and if it exceeds 100 μm, the surface roughness of the wiping layer of the film is not formed. As a result, the wiping function required as a product is lowered. In particular, it becomes difficult to capture fine particles on the order of nm.

  The material of the plastic fine particles can be appropriately selected from resins having appropriate hardness. For example, polymethacrylic acid ester, polystyrene, polyolefin, phenol resin, epoxy resin, acrylonitrile-butadiene-styrene resin, high density polyethylene resin, urea resin, polyester resin, polyvinyl chloride, polyamide, polycarbonate and the like. Further, those obtained by surface modification of these fine particles, for example, metal coating or treatments such as introduction of a functional group may be used. Further, the above-mentioned plastic fine particles may be mixed in order to ensure that fine particles of an inorganic material such as spherical glass or spherical ceramic are supported on the substrate.

  Commercially available plastic fine particles may be used. For example, “Chemisnow (trade name)” manufactured by Soken Chemical Co., Ltd. can be used.

As the binder , conventionally known thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, ultraviolet curable resins, visible light curable resins, and mixtures thereof can be used. Those conventionally used as binders for wrapping films are preferred.

  These binders may be those that provide a hardness of 15 to 90, preferably 50 to 85 on Shore D after curing in the case of thermosetting at room temperature.

  When the binder is a thermoplastic resin, those having a softening temperature of 150 ° C. or less, an average molecular weight of 10,000 to 300,000, and a degree of polymerization of at least about 50 to 200, particularly about 200 to 700 are preferred.

  Specifically, vinyl chloride-vinyl acetate copolymer, vinyl chloride copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, Vinyl chloride-acrylonitrile copolymer, acrylate ester-acrylonitrile copolymer, acrylate ester-vinylidene chloride copolymer, acrylate ester-styrene copolymer, methacrylate ester-acrylonitrile copolymer, methacrylate ester-chloride Vinylidene copolymer, methacrylate ester-styrene copolymer, urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, ethylcellulose, methylcellulose, propylcellulose, methylethylcellulose, carboxymethylcellulose, acetylcellulose, etc.), styrene-butadiene A copolymer, a polyester resin, a polycarbonate resin, a chlorovinyl ether-acrylic acid ester copolymer, an amino acid resin, various synthetic rubber thermoplastic resins, and a mixture thereof are used.

  On the other hand, when the binder is a thermosetting resin or a reactive resin, the molecular weight is 200,000 or less in the state of the coating solution, and the molecular weight is infinite by reaction such as condensation addition by heating and humidifying after coating and drying. Is preferably used. Among these resins, those that do not soften or melt until the resin is thermally decomposed are particularly preferable.

  Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane resin, polyester resin, polyurethane polycarbonate resin, urea resin, melamine resin, alkyd resin, silicon resin, acrylic reaction resin (electron beam curable resin), epoxy- Polyamide resin, Nitrocellulose-melamine resin, Mixture of high molecular weight polyester resin and isocyanate prepolymer, Mixture of methacrylate ester copolymer and diisocyanate prepolymer, Mixture of polyester polyol and polyisocyanate, Urea formaldehyde resin, Low molecular weight glycol / High molecular weight diol / triphenylmethane triisocyanate mixtures, polyamine resins, polyimine resins and mixtures thereof.

  As a curing agent for the thermosetting resin, polyisocyanate is preferably used. Specific examples of the polyisocyanate include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, O-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and the like. Isocyanates, products of the isocyanates with polyalcohols, di- to 10-mer polyisocyanates formed by condensation of isocyanate chains, and polyisocyanate-polyurethane products with terminal functional groups being isocyanates And the like. The molecular weight of these polyisocyanates is 100 to 20000 on the number average.

Production of Wiping Film The wiping film of the present invention is produced by forming a wiping layer containing plastic fine particles and a binder on one surface of a base film and curing the layer. The wiping layer is generally formed by mixing and dispersing plastic fine particles in a binder solution to prepare a coating solution in advance, coating the coating solution on the surface of the substrate film, and drying.

  The mixing ratio of the plastic fine particles and the binder is 70/100 to 350/100 in terms of the weight ratio of the non-volatile content (the state after removing the solvent, for example, the state after removing methyl ethyl ketone and toluene in the examples). Preferably, the ratio is 100/100 to 200/100. When the mixing ratio is less than 70/100, most of the surface of the wiping layer of the film is covered with a binder, and sufficient uneven structure required for product design cannot be obtained. If it exceeds, the plastic fine particles are easily separated from the wiping layer of the film.

  When mixing, a plurality of types of binders may be used in combination, and if necessary, as additives, dispersants, coupling agents, lubricants, antistatic agents, antioxidants, antifungal agents, coloring Conventional additives such as agents and solvents are added. The order of adding each component, the dispersion temperature (0 to 80 ° C.), and the like can be set as appropriate.

  For example, the order of addition of the additives is as follows. First, a coupling agent and a dispersant are added together at the start of mixing of the plastic fine particles and the binder, and it is estimated that the uniform dispersion is completed. It is carried out by adding an antistatic agent or the like almost simultaneously. The dispersion temperature at that time is determined in consideration of, for example, the volatilization temperature of the solvent in the coating solution. For example, when methyl ethyl ketone or toluene is the main component, the dispersion temperature is maintained at 20 to 50 ° C. A normal kneader can be used to prepare the coating solution.

  As a method of applying the coating solution to the surface of the base film, the viscosity of the coating solution is adjusted appropriately, and then a gravure coater, air doctor coater, blade coater, rod coater, knife coater, squeeze coater, impregnation machine, reverse roll coater. , Transfer roll coater, kiss roll coater, cast coater, spray coater, slot orifice coater (curtain coater, fountain coater), electrostatic powder coater, electrodeposition coating, powder electrodeposition coating, vacuum plating method, extrusion coater, etc. A micro replication method, a PVD method, a CVD method, various vapor deposition methods, and the like can be used.

  Specific explanations of these methods are given in “Coating Method” (published on October 30, 1979) published by Tsuji Shoten, “New Trends in Thin Film Technology” (issued July 15, 1997) It is described in detail on page 135. According to these, it is understood that the viscosity of the coating solution in each coater suitable for carrying out the present invention may be set under the following conditions.

  The order of application of these coating liquids can be arbitrarily selected, and corona discharge treatment or the like may be performed to improve adhesion to the undercoat layer or the film-like substrate before application of the desired liquid.

  After apply | coating a coating solution to a film-form base material, this is dried, a binder is hardened, and a wiping film is obtained. Curing of the binder is generally performed by heating.

  In the obtained wiping film, the thickness of the wiping layer is 1 to 200 μm, more preferably 2 to 20 μm. When the thickness of the wiping layer is less than 1 μm, the wiping layer formed on the substrate is likely to cause delamination and the like, and when the thickness exceeds 200 μm, the raw materials such as plastic fine particles and binders are obtained in comparison with the wiping function obtained. This is because the amount used is bulky and the film for this purpose is expensive.

  The center line average surface roughness (Ra) of the wiping layer is 50 μm or less, preferably 0.01 to 5 μm (cutoff value: 80 μm). This is because if the surface roughness exceeds 50 μm, the surface of the wiping layer of the film becomes too rough. Incidentally, in the object to be wiped such as a magnetic disk, the surface roughness is required to be nano-base and further angstrom order, and the surface roughness of the wiping layer of the film needs to be adjusted with high accuracy accordingly. .

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Example 1
Raw materials A to D shown in Table 2 were put into a tank, and dispersed and kneaded for 60 minutes at 1800 rpm using a high-speed shear mixer, and it was confirmed that plastic fine particles were uniformly dispersed. Thereafter, the raw material E was added, and stirring was further performed for 15 minutes. Thereafter, filtration was performed to obtain a coating solution having a solid content concentration of 35.0%.

As a film-like substrate, a polyethylene terephthalate (PET) film, manufactured by Teijin Limited, model number: G2-24, average thickness: 23.3 μm, breaking strength: length 28 kg / mm ² -width 29 kg / cm ² , breaking elongation: Length 125%-width 110%, surface roughness (Ra): 0.023 μm, thermal shrinkage (150 ° C. × 30 minutes): length 1.8% —width 0.3%, haze: 3.0%, friction Coefficient: static 0.35-motion 0.33 was prepared.

  The coating solution was applied to the surface of the film substrate by a direct gravure coating method. The coating amount was such that the thickness of the wiping layer after curing was 6 μm. Next, this was placed in an atmosphere of 40 to 130 ° C. for 5 to 300 seconds to dry the coating solution, and then the wiping layer was cured. After curing, the surface roughness (Ra) of the wiping layer surface was measured and found to be 0.203 μm.

  The obtained wiping film was attached to a texturing grinder manufactured by Hitachi Electronics Engineering. Then, the surface of the 3.5-inch NI-P plated aluminum substrate was wiped under the conditions shown in Table 3. And the surface roughness of the base material was measured before and after the process. The results are shown in Table 4.

Comparative Example 1
3.5 inches are obtained in the same manner as in Example 1 except that a conventional wrapping film (abrasive grains: aluminum oxide having an average particle diameter of 0.3 μm, Ra on the polishing layer surface: 0.045 μm) is used instead of the wiping film. The surface of the NI-P plated aluminum substrate was polished.

  And the surface roughness of the board | substrate was measured before and after the process. The results are shown in Table 4.

Comparative Example 2
3.5 inch NI− in the same manner as in Example 1 except that a conventional wrapping film (abrasive grains: aluminum oxide having an average particle diameter of 1 μm, Ra of the polishing layer surface: 0.162 μm) is used instead of the wiping film The surface of the P-plated aluminum substrate was polished.

  And the surface roughness of the board | substrate was measured before and after the process. The results are shown in Table 4.

Comparative Example 3
3.5 inch NI− in the same manner as in Example 1 except that a conventional wrapping film (abrasive grains: aluminum oxide having an average particle diameter of 2 μm, Ra of the polishing layer surface: 1.56 μm) is used instead of the wiping film The surface of the P-plated aluminum substrate was polished.

  Then, the surface roughness of the substrate was measured before and after polishing. The results are shown in Table 4.

  In the surface treatment using the wiping film of the example, it was confirmed that the surface roughness of the substrate was not changed before and after the treatment, and the treated surface was not damaged such as scratches.

It is sectional drawing which shows an example of the wiping film of this invention.

1 ... film-like substrate,
2 ... Plastic fine particles,
3 ... Binder resin,
4 ... Wiping layer.

Claims (4)

  A wiping film comprising a flexible film-like substrate and a wiping layer formed on one surface of the substrate, wherein the wiping layer comprises a binder and plastic fine particles dispersed therein.   The wiping film according to claim 1, wherein the plastic fine particles have an average particle diameter of 0.01 to 100 μm and a Rockwell hardness of M10 to M130.   The wiping film according to claim 1 or 2, wherein a weight ratio of the plastic fine particles to the binder is 70/100 to 350/100.   The wiping film according to any one of claims 1 to 3, wherein a center line average surface roughness (Ra) of the surface of the wiping layer is 50 µm or less.

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