JP2005182956A - Manufacturing method and apparatus of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably manufacture a low noise high density application type magnetic recording medium with a high working rate by stabilizing grinding force of a grindstone. <P>SOLUTION: A magnetic coating material including ferroelectric powder and binder is applied to a non-magnetic band type flexible supporter and a magnetic layer is formed, after that, the magnetic layer is ground by the grindstone 14. Surroundings of a grinding part of the grindstone is kept by nitrogen atmosphere during grinding. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for manufacturing a magnetic recording medium, and more particularly to a method and apparatus for manufacturing a magnetic recording medium suitable for manufacturing a low-noise and high-density coating type magnetic recording medium.

  As magnetic recording media for audio, video, broadcasting, and computers, magnetic tapes that are coated with a magnetic paint containing a ferromagnetic powder and a binder are widely used. In the manufacture of such magnetic tape, the surface of the magnetic layer is applied by applying a grinding wheel such as a rotating diamond wheel to the magnetic layer of the magnetic tape in order to prevent clogging of the magnetic head in use and to prevent wear of the magnetic head. In some cases, the fine protrusions or the like are removed (grinding) (see, for example, Patent Document 1).

  By the way, in such grinding, there is a problem that the grinding force gradually decreases. This decrease in grinding force is caused by the fact that diamond abrasive grains that were initially sharp at the tip gradually wear out as the grinding process proceeds, and the tip of the abrasive grain becomes flat, and as a result, the grinding force gradually decreases. It is thought to go. In addition, this phenomenon of reduced grinding force is thought to be affected by the fact that shavings removed by grinding process accumulate between diamond grains on the grinding wheel surface, causing clogging of the abrasive grains. It has been.

As a countermeasure, conventionally, when clogging of abrasive grains occurs, the surface of the grinding wheel is wiped with a cloth soaked in a solvent that can dissolve the magnetic paint, etc. to eliminate clogging of the abrasive grains. A certain effect was obtained.
Japanese Patent Laid-Open No. 62-172532

  However, even if the conventional method can cope with the clogging of the abrasive grains, the effect of reducing the wear and wear of the diamond abrasive grains and suppressing the reduction of the grinding force is hardly obtained.

  On the other hand, in the case of a grinding wheel such as a diamond wheel used for general grinding applications such as glass and ceramic grinding, dressing or grinding liquid ( In the manufacture of a magnetic recording medium, it is difficult to adopt such means.

  In other words, since dressing causes contamination of the magnetic recording medium, dressing on the machine cannot be adopted, and it is necessary to remove the grinding wheel and perform dressing elsewhere, increasing the burden on the operator, increasing downtime, etc. Therefore, productivity is remarkably bad. In addition, the use of a grinding fluid (coolant) cannot be adopted because of adverse effects such as contamination of the magnetic recording medium.

  The present invention solves the above-mentioned conventional problems (problems) and stabilizes the grinding force of the grinding wheel, thereby making it possible to manufacture a low-noise, high-density coating type magnetic recording medium stably and at a high operating rate. It is an object of the present invention to provide a method and apparatus for manufacturing a magnetic recording medium.

  In order to achieve the above object, the present invention forms a magnetic layer by coating a nonmagnetic belt-like flexible support with a magnetic paint containing a ferromagnetic powder and a binder, and then forming the magnetic layer. In a method for manufacturing a magnetic recording medium in which a grinding wheel is ground with a grinding wheel, the periphery of the grinding portion of the grinding wheel is maintained in a nitrogen atmosphere during the grinding, and the method is used for the method. An apparatus for manufacturing a magnetic recording medium is provided.

  According to the present invention, during grinding, the periphery of the grinding point of a grinding wheel such as a diamond wheel is maintained in a nitrogen atmosphere, so wear due to oxidation of grinding grains (diamond grains etc.) on the grinding wheel surface can be significantly reduced, The grinding force of the grinding wheel can be stabilized. As a result, a low-noise, high-density coated magnetic recording medium can be manufactured stably and at a high operating rate.

  As described above, according to the present invention, the periphery of the grinding wheel such as a diamond wheel is maintained in a nitrogen atmosphere during grinding, so that wear due to oxidation of the grinding abrasive grains (diamond abrasive grains, etc.) on the grinding wheel surface is maintained. Can be remarkably reduced, and the grinding force of the grinding wheel can be stabilized. As a result, a low-noise, high-density coated magnetic recording medium can be manufactured stably and at a high operating rate.

  Preferred embodiments of a method and apparatus for manufacturing a magnetic recording medium according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a configuration of a magnetic tape grinding apparatus 10 which is a magnetic recording medium manufacturing apparatus according to the present invention.

  This magnetic tape grinding apparatus 10 winds a magnetic tape 1 that is a magnetic recording medium on which a magnetic layer is formed, around a diamond wheel 14 that is rotationally driven at a predetermined speed (circumferential speed) while transporting the magnetic tape 1 at a predetermined speed. An apparatus for grinding the surface of the tape 1.

  The inside of the apparatus main body 12 has a nitrogen atmosphere necessary for the diamond wheel 14 and the magnetic tape 1 wound around the diamond wheel 14 so that the periphery of the grinding portion of the diamond wheel 14 can be maintained in a nitrogen atmosphere during grinding. An unnecessary space other than the space 16 is configured to be minimized.

  That is, the nitrogen atmosphere space 16 forms a space having a predetermined inner diameter larger than the outer diameter of the diamond wheel 14 provided around the diamond wheel 14 and a traveling path of the magnetic tape 1 provided in the tangential direction of the diamond wheel 14. It is formed from space. With this configuration, the nitrogen gas supplied from the nitrogen supply port 18 overflows to the outside of the apparatus body 12 while filling the nitrogen atmosphere space 16.

  Inside the apparatus main body 12, a probe (sensor) of the oxygen concentration measuring device 20 is disposed in the vicinity of the grinding portion of the diamond wheel 14 so that the oxygen concentration at the time of grinding can be measured.

  Next, the magnetic tape 1 (magnetic recording medium) used in the present invention will be described. In the magnetic tape 1, a magnetic layer is formed by coating a magnetic coating material containing a ferromagnetic powder and a binder on a nonmagnetic belt-like flexible support.

  As the nonmagnetic belt-like flexible support, generally, polyethylene terephthalate (PET) having a predetermined width, a length of 45 to 20000 m, and a thickness of 2 to 200 μm, polyethylene-2,6-naphthalate, cellulose diacetate, Cellulose triacetate, cellulose acetate propionate, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide, polyamide and other plastic films, paper, polyethylene, polypropylene, ethylene butene copolymer and other α-polyolefins having 2 to 10 carbon atoms A flexible strip made of paper or the like coated or laminated on the surface or a strip having a processed layer formed on the surface of the strip can be used.

Various materials can be used as the ferromagnetic powder used in the magnetic coating material. When the ferromagnetic powder is hexagonal ferrite, the ferromagnetic powder having a plate diameter of 35 nm or less and a plate ratio of 2 or more is used. Is a ferromagnetic metal powder, those having a major axis length of 60 nm or less and an axial ratio of 2 or more can be preferably used. As the particle size of the ferromagnetic powder, those having an average primary particle volume of 10,000 nm ³ or less can be preferably used.

  The solvent in which the ferromagnetic powder is immersed is preferably a solution containing cyclohexanone. The content of cyclohexanone is preferably 30 to 100% by weight of the total amount of solvent. As a solution other than cyclohexanone, it is preferable to use methyl ethyl ketone, toluene, butyl acetate or the like.

  As an application means for the magnetic paint, a roller coating method, a dip coating method, a fountain coating method, etc. can be adopted in the application system, and an air knife coating method, a blade coating method, a bar coating method, etc. can be adopted in the metering system. In addition, an extrusion coating method, a slide bead coating method, a curtain coating method, and the like can be adopted as the application system and the weighing system in charge of the same part.

  The thickness of the magnetic layer of the magnetic recording medium to be produced is preferably 0.02 to 3 μm, more preferably 0.02 to 0.2 μm as a dry film. Further, it is preferable to have a layer structure in which a nonmagnetic layer mainly composed of a nonmagnetic powder and a binder is provided between the magnetic layer and the nonmagnetic support. In particular, in the configuration in which the magnetic layer is a thin layer, it is possible to reduce coating stripes by crushing the agglomerated magnetic material, so it is only necessary to improve the media performance by suppressing the C / N drop in the short wavelength region. There is also an advantage that productivity can be improved.

  The magnetic layer of the applied magnetic paint is dried after the treatment for orienting the ferromagnetic powder, that is, the magnetic field orientation treatment. The magnetic layer after drying is subjected to a surface smoothing treatment. This process is performed by, for example, a super calendar roll.

  In this state, since 90% by mass or more of the curing agent in the magnetic layer is in an unreacted state, curing treatment was performed, and 50% by mass or more, preferably 80% by mass or more of the curing agent was reacted. It is preferable to perform grinding later.

  Grinding may be performed with the wide belt-like flexible support as it is, but usually it is performed after cutting to a predetermined product width (for example, 12.65 mm, 25.4 mm, 3.81 mm, etc.). Is. This process can be performed with a known slitter.

  In the grinding process, as shown in FIG. 1 described above, the magnetic tape 1 is wound at a predetermined winding angle so that the magnetic layer side is in contact with a rotating disk-shaped (No. 1 flat grinding wheel) diamond wheel 14. At the same time, a predetermined tension is applied.

  As the diamond wheel 14, a metal bond type diamond wheel can be preferably used. Depending on conditions, a vitrified diamond wheel, a resin bond diamond wheel, or an electrodeposition diamond wheel can be used.

  The grain size of diamond abrasive grains used in this diamond wheel is preferably # 600 to # 5000, more preferably # 800 to # 2000. If the grain size of the diamond abrasive grains is too large, scratches on the magnetic layer become a problem, and if the grain size of the diamond abrasive grains is too small, the grinding ability is low and not preferred.

  The diamond wheel bond material, concentration (concentration), and the like may be selected as appropriate according to the composition of the magnetic layer. The winding angle and the relative speed in grinding may be selected appropriately depending on the outer diameter of the diamond wheel, the composition of the magnetic layer, and the like.

  As the nitrogen atmosphere around the grinding site to be maintained during grinding, the oxygen concentration is preferably 0.5%, the oxygen concentration is more preferably 0.2%, and the oxygen concentration is 0.1%. The state is more preferable. In order to obtain such an oxygen concentration, it is necessary to maintain the flow rate of nitrogen gas supplied to the nitrogen supply port 18 in an appropriate range. As a supply source of the nitrogen gas to be supplied, known means such as a nitrogen cylinder or a nitrogen gas supply device that supplies nitrogen gas after being vaporized from liquid nitrogen can be employed.

  Next, manufacturing of the magnetic tape 1 using the magnetic tape grinding apparatus 10 (grinding of the magnetic tape 1) will be described with reference to FIG. The diamond wheel 14 is rotationally driven clockwise at a predetermined speed (circumferential speed). Further, a predetermined flow rate of nitrogen gas is supplied from the nitrogen supply port 18 to maintain the nitrogen atmosphere space 16 in a predetermined nitrogen atmosphere. The magnetic tape 1 is fed from a tape supply means (usually a feed roll) (not shown), supplied from the opening 12A on the left side of the apparatus main body 12, wound around the diamond wheel 14, and ground (upper surface) is ground. And it discharges | emits from the opening 12B of the right side of the apparatus main body 12, and accommodates in the tape storage means (usually winding roll) which is not shown in figure.

  During grinding, the vicinity of the processing point is maintained in a predetermined nitrogen atmosphere, so that wear and abrasion due to oxidation of diamond abrasive grains on the surface of the diamond wheel 14 is suppressed. Therefore, the grinding force of the diamond wheel 14 can be stabilized and the diamond wheel 14 can be used without dressing for a very long time. As a result, a low-noise, high-density coated magnetic recording medium can be manufactured stably and at a high operating rate.

  As mentioned above, although embodiment of the manufacturing method and apparatus of the magnetic recording medium concerning this invention was described, this invention is not limited to the said embodiment, Various aspects can be taken.

  For example, a configuration is adopted in which nitrogen gas is supplied to suppress wear and abrasion due to oxidation of diamond abrasive grains, but other inert gases such as argon gas can also be used, and the same effect can be obtained. The effect is obtained. Therefore, it can be said that this configuration is also within the equivalent range of the present invention.

  In addition to the diamond wheel 14, a CBN wheel or the like can be used as a grinding wheel. Even for such a wheel, similar actions and effects can be obtained by maintaining the vicinity of the machining point in a predetermined nitrogen atmosphere.

  Further, although the magnetic tape 1 is employed as the magnetic recording medium, the present invention can also be applied to a disk-shaped one such as a flexible disk. In this case, various types of cup-shaped grindstones can be employed in addition to the No. 1 flat grindstone of FIG.

  Next, examples of the present invention will be described in comparison with comparative examples. In the following examples, “parts” means “parts by weight”. A layer structure in which a nonmagnetic intermediate layer mainly composed of a nonmagnetic powder and a binder was provided between the magnetic layer and the nonmagnetic support was adopted.

  Using a barium ferrule with a plate diameter of 26 nm and a plate ratio of 3 as the ferromagnetic powder, the ferromagnetic powder and the binder solution were brought into contact with an open kneader when preparing the magnetic liquid, kneaded to prepare the liquid, and then dispersed. A treated magnetic paint was used.

  The structure of the magnetic layer is shown below (magnetic solution and additive solution are shown; others are omitted).

a) Additive paste liquid (additive solution) (common to Examples 1 to 3)
α-alumina (particle size 0.18 μm) 4.5 parts carbon black (particle size 0.10 μm) 0.5 parts MR110 0.45 parts cyclohexanone 9.2 parts The additive paste liquid was carbon black: alumina: MR110: The ratio was cyclohexanone = 5: 45: 4.5: 50.5.

b) Magnetic liquid 100 parts of ferromagnetic powder Plate diameter 26 nm, plate ratio 3, average primary particle volume 3805 nm ³
SBET 60 m ^{2 /} g, pH 7.9
Hc187856A / m (2360 Oe)
σs 49A ・ m ² / kg
True specific gravity 5.1g / ml, apparent specific gravity 0.7g / ml
MR110 10 parts Methyl ethyl ketone 20 parts Cyclohexanone 170 parts The magnetic coating solution was prepared as liquid A in a ratio of ferromagnetic powder: cyclohexanone = 100 parts: 150 parts.

  Separately, as a solution B, a binder solution of MR110: cyclohexanone: methyl ethyl ketone = 10: 20: 20 (liquid solid concentration 20%) prepared by a dissolver type stirrer was prepared and used by mixing with the liquid A.

  A polyethylene terephthalate (PET) sheet having a width of 1000 mm and a thickness of 15 μm was used as a nonmagnetic belt-like flexible support. As an application means for the magnetic paint, an extrusion coating apparatus was used so that the film thickness at the time of coating was 3 μm.

  Magnetic field orientation treatment, drying, and surface smoothing treatment of the magnetic tape after coating were performed under general conditions. Then, it cut | judged with the slitter to the width of 12.65 mm, and obtained the magnetic tape 1. FIG.

  The diamond wheel 14 used in the grinding process has a disk shape (No. 1 flat shape), and has an outer shape with an outer diameter of 70 mm, a width of 25.6 mm, and a bond layer thickness of 1.5 mm. The abrasive grain size is # 1200, and the concentration is 50.

  The grinding conditions were as follows. The rotation speed of the diamond wheel 14 was 1900 rpm, the winding angle was 90 degrees, and the traveling of the magnetic tape 1 was 400 m / min in the direction opposite to the rotation direction of the diamond wheel 14.

  The measured value with the oxygen concentration measuring device 20 in the nitrogen atmosphere space 16 of the example was 0.2% oxygen concentration.

  As a comparative example, the supply of nitrogen gas was stopped, and grinding was performed with the nitrogen atmosphere space 16 as an air atmosphere.

  As evaluation items of the examples and comparative examples, the wear and wear of diamond abrasive grains at a predetermined processing amount and the wear amount of the magnetic tape 1 at a predetermined processing amount were adopted.

  As an evaluation of wear and abrasion of the diamond abrasive grains, the surface of the diamond wheel 14 was measured with a stylus type surface roughness meter to determine the surface roughness Ra.

  As an evaluation of the wear amount of the magnetic tape 1, the method shown in FIG. 2 was adopted. That is, while the magnetic tape 1 was running, it was brought into contact with the ferrite bar F, and the wear volume was measured. In FIG. 2, as the ferrite bar F, a rectangular column (a cross section is square), one side is 4.5 mm, and the length is 18 mm (manufactured by Sumitomo Special Metals Co., Ltd., model number: H4R2B) is used. The inclination angle α with respect to the horizontal was 12 degrees on both the approach side and the exit side. The tape 1 having a length of 300 m was caused to travel 300 reciprocations under the condition that the running speed of the tape 1 was 180 m / min and the tension of the tape 1 was 100 g / 12.7 mm width. ) Was calculated.

  FIG. 3 is a graph of evaluation results of wear and abrasion of diamond abrasive grains at a predetermined processing amount, the vertical axis is the surface roughness Ra (unit: μm), and the horizontal axis is a roll of the magnetic tape 1 wound by 10,000 m. The number of processes.

FIG. 4 is a graph of the evaluation result of the wear amount of the magnetic tape 1 at a predetermined processing amount, and the vertical axis indicates the wear amount (unit: m inch ³ / ft, that is, (25.4 × 10 ⁻³ mm) ³ / 30 cm), and the horizontal axis represents the number of rolls wound with 10,000 m of the magnetic tape 1.

  In FIG. 3, the surface roughness Ra tends to decrease as the number of treatments increases in the processed state in air (comparative example). Therefore, it is presumed that diamond abrasive grains are worn and worn, and the tips of the abrasive grains are flattened. On the other hand, in the processed state in nitrogen (Example), the surface roughness Ra is less reduced than in the air. Therefore, it is presumed that the progress of wear and wear of the diamond abrasive grains is suppressed by the nitrogen atmosphere.

  In FIG. 4, in the processed state in the air (comparative example), the amount of wear tends to increase as the number of treatments increases. Therefore, it is presumed that the diamond abrasive grains are worn and worn by the oxidation reaction, and the tips of the abrasive grains are flattened. On the other hand, the amount of wear in the processed state in nitrogen (Example) does not change compared to that in the air. Therefore, it is presumed that the progress of abrasion and wear of diamond abrasive grains due to the oxidation reaction is suppressed by the nitrogen atmosphere.

Sectional drawing which shows the structure of the manufacturing apparatus of the magnetic-recording medium based on this invention Schematic showing how to evaluate the amount of magnetic tape wear The graph which shows the result of an Example The graph which shows the result of an Example

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Magnetic tape, 10 ... Magnetic tape grinding apparatus (Magnetic recording medium manufacturing apparatus), 12 ... Apparatus main body, 14 ... Diamond wheel, 16 ... Nitrogen atmosphere space, 18 ... Nitrogen supply port, 20 ... Oxygen concentration measuring device

Claims (2)

A method of manufacturing a magnetic recording medium, comprising: forming a magnetic layer by coating a magnetic coating material containing a ferromagnetic powder and a binder on a non-magnetic belt-like flexible support; and then grinding the magnetic layer with a grinding wheel In
A method of manufacturing a magnetic recording medium, wherein a periphery of a grinding portion of the grinding wheel is maintained in a nitrogen atmosphere during the grinding. In an apparatus for producing a magnetic recording medium comprising a grinding wheel for grinding a magnetic layer in which a magnetic coating material containing a ferromagnetic powder and a binder is coated on a nonmagnetic belt-like flexible support,
An apparatus for manufacturing a magnetic recording medium, wherein a periphery of a grinding portion of the grinding wheel is maintained in a nitrogen atmosphere.

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