Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
  • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
  • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
  • C08G73/22—Polybenzoxazoles
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G75/00—Macromolecular compounds obtained by reactions forming a linkage containing sulfur with or without nitrogen, oxygen, or carbon in the main chain of the macromolecule
  • C08G75/32—Polythiazoles; Polythiadiazoles
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
  • G11B5/739—Magnetic recording media substrates
  • G11B5/73923—Organic polymer substrates

Definitions

• the present invention relates to the art of flexible magnetic recording media, such as floppy disks and magnetic tapes.
• Flexible magnetic recording media typically contain a flexible polymer substrate and a magnetizable surface layer.
• substrates include poly(ethylene terephthalate) (PET) polymers and poly(ethylene naphthalate) (PEN) polymers (commercially sold as Teonex TM film by Teijin).
• PET poly(ethylene terephthalate)
• PEN poly(ethylene naphthalate)
• Teonex TM film commercially sold as Teonex TM film by Teijin.
• the surface layer usually contains either a continuous thin layer of a magnetizable material or a magnetizable particulate held on the substrate by a binder.
• common particulate materials include oxides of iron and/or chromium, metallic particles and ferrite compounds of barium, lead and strontium.
• common binders include urethanes, acrylics and epoxy resins.
• the substrate in the medium is usually more bulky than the magnetizable surface. Therefore, a change that substantially lowers the volume of substrates in the medium can substantially reduce the volume of the entire medium.
• the substrate may stretch out of shape during use. Such stretching distorts the signal. If the stretching is not uniform, it can stretch a magnetic disc into an asymmetrical shape, making it difficult for read-heads to track data on the disc. If the substrate has a low yield point, then the distortion may become permanent.
• One aspect of the present invention is a flexible magnetic recording medium comprising:
• a substrate (a) a substrate; and b) a magnetizable surface layer adhered to the substrate characterized in that the substrate contains a polybenzazole polymer that can form lyotropic liquid crystalline domains when dissolved in acid.
• the polybenzazole polymer can be selected to provide a selected combination of high tensile strength, high tensile modulus, temperature stability, etc.
• the magnetic media can be used in an ordinary mannerto record electronic data.
• the present invention relates to magnetic recording media.
• Each magnetic recording medium contains a substrate that has a film containing a polybenzazole polymer.
• polymer shall refer to both homopolymers and
• Suitable polybenzazole polymers and polymerfilms are well-known in the art. Polybenzazole polymers are described in references such as Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Patent 4,703, 103 (October 27, 1987); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Patent 4,533,692 (August 6, 1985); Wolfe etal., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, U.S. Patent 4,533,724 (August 6, 1985); Wolfe, Liquid
• the polymer may contain AB-PBZ mer units (as represented in Formula 1 (a)) and/or AA/BB-PBZmer units (as represented in Formula 1(b))
• Each Ar represents an aromatic group selected so that the polymer forms lyotropic liquid crystalline domains when dissolved in acid.
• the aromatic group may be heterocyclic, such as a pyridinylene group, but it is preferably carbocyclic.
• the aromatic group may be a fused or unfused polycyclic system, but is preferably a single six-membered ring. Size is not critical, but the aromatic group preferably contains no more than about 18 carbon atoms, more preferably no more than about 12 carbon atoms and most preferably no more than about 6 carbon atoms. Examples of suitable aromatic groups include phenylene moieties, tolylene moieties, biphenylene moieties and bis-phenylene ether moieties.
• -mer units is preferably a 1,2,4,5-phenylene moiety or an analog thereof.
• AB-mer,units is preferably a 1 ,3,4-phenylene moiety or an analog thereof:
• Each Z is independently -O-, -S- or -NR- wherein R is hydrogen, an alkyl group or an aromatic group.
• Each DM is independently a bond or a divalent organic moiety selected so that the polymer forms lyotropic liquid crystalline domains when dissolved in acid.
• the divalent organic moiety is preferably an aromatic group (Ar) as previously described. It is most preferably a 1 ,4-phenylene moiety or an analog thereof.
• each azole ring is bonded to adjacent carbon atoms in the aromatic group, such that a five-membered azole ring fused with the aromatic group is formed.
• the azole rings in AA/BB-mer units may be in cis- or trans-position with respect to each other, as illustrated in 1 1 Ency. Poly. Sci. & Eng., supra, at 602.
• the polymer preferably consists essentially of either AB-PBZ mer units or AA/BB- PBZ mer units, and more preferably consists essentially of AA/BB-PBZ mer units.
• the polybenzazole is usually soluble in strong acids such as methanesulfonic acid, polyphdsphoric acid or 100 percent sulfuric acid. It forms anisotropic solutions that contain lyotropic liquid crystalline domains when its concentration is higher than a critical percentage.
• the polymer is preferably selected such that it is essentially stable for at least about 45 minutes up to about 300°C, more preferably at least about 400°C, and most preferably at (east about 500°C.
• Preferred mer units are illustrated in Formulae 2 (a)-(h).
• the polymer preferably consists essentially of mer units selected from those illustrated in 2 (a)-(h), and most preferably consists essentially of a number of identical units selected from those illustrated in 2 (a)-(c).
• Each polymer molecule preferably contains on average at least about 25 mer units, more preferably at least about 50 mer units and most preferably at least about 100 mer units.
• the intrinsic viscosity of rigid AA/BB-PBZ polymers in methanesulfonic acid at 25°C is preferably at least about 10 dL/g, more preferably at least about 15 dL/g and most preferably at least about 20 dL/g. For some purposes, an intrinsic viscosity of at least about 25 dL/g or 30 dL/g may be best. Intrinsic viscosity of 60 dL/g or higher is possible, but the intrinsic viscosity is preferably no more than about 40 dL/g.
• the intrinsic viscosity of semi-rigid AB-PBZ polymers is preferably at least about 5 dL/g, more preferably at least about 10 dL/g and most preferably at least about 15 dL/g.
• Suitable polymers can be synthesized by known procedures, such as those described in Wolfe et al., U.S. Patent 4,533,693 (August 6, 1985); Sybert et al., U.S. Patent 4,772,678 (September 20, 1988); Harris, U.S. Patent 4,847,350 (July 1 1 , 1989); and Ledbetter et al., "An Integrated Laboratory Process for Preparing Rigid Rod Fibers from the Monomers," The Materials Science and Engineering of Rigid-Rod Polymers at 253-64 (Materials Res. Soc. 1989).
• suitable monomers are reacted in a solution of non-oxidizing and dehydrating acid under non-oxidizing atmosphere with vigorous mixing and high shear at a temperature that is increased in step-wise orramped fashion from no more than 120°C to at least 190°C.
• suitable AA-monomers include terephthalic acid and analogs thereof.
• suitable BB-monomers include 4,6-diaminoresorcinol, 2,5-diaminohydroquinone, 2,5-diamino-1 ,4-dithiobenzene and analogs thereof, typically stored as acid salts.
• Suitable AB-monomers include 3-amino-4 -hydroxybenzoic acid, 3-hydroxy-4-aminobenzoic acid, 3-amino-4-thiobenzoic acid, 3-thio-4 ⁇ -aminobenzoic acid and analogs thereof, typically stored as acid salts.
• Polybenzazole polymers are typically synthesized in an acid solution, known as a dope, with a suitable acid such as polyphosphoric acid.
• the dope should contain a high enough concentration of polymer for the polymer to coagulate to form a film of the desired thickness without substantial flaws.
• the concentration of polymer in the dope is preferably high enough to provide an anisotropic dope that contains liquid-crystalline domains.
• the concentration of the polymer is preferably at least about 7 weight percent, more preferably at least about 10 weight percent and most preferably at least about 14 weight percent.
• the maximum concentration is limited primarily by practical factors, such as polymer solubility and dope viscosity.
• the concentration of polymer is seldom more than 30 weight percent, and usually no more than about 20 weight percent.
• the dope may be converted to a polybenzazole film or sheet by known methods, such as by: (i) extruding the dope out of a die; (ii) orienting or stretching the dope film uniaxially, biaxially or multiaxially; and (iii) coagulating the dope by contact with a diluent such as water.
• the die may be a slit or annular die.
• the dope film may be stretched by any ordinary means, such as by tentering or by a bubble process. Examples of suitable film manufacturing techniques are described in: Chenevey, U.S. Patent 4,487,735 (December 1 1 , 1984); Chenevey, U.S.
• Patent 4,898,924 (February 6, 1990); Harvey et al., U.S. Patent 4,939,235 (July 3, 1990); Harvey et al., U.S. Patent 4,934,285 (October 16, 1990); and Pierini et al., U.S. Patent Application Ser. No.07/670,135 (filed March 15, 1991).
• a dope film is extruded through a slit die.
• the film is stretched in the machine direction by rollers and stretched in the transverse direction by tentering to achieve desired tensile properties. It is coagulated by contact with a non-solvent under restraint to minimize shrinkage, washed to remove the remaining solvent, and dried under restraint to minimize shrinkage.
• the film is preferably stretched to at least 150 percent of its original length and width. It may be stretched up to 7 or more times its original length and/or width.
• the ratio of stretching in the machine direction (along the length of the film) to stretching in the transverse direction (along the width of the film) may be selected to provide a film with higher tensile strength or modulus along its length, higher tensile strength or modulus along its width, or about equal properties in all directions.
• the tensile strength of the film is preferably at least about 10 ksi (69 MPa), more preferably at ieast about 25 ksi (170 MPa), highly preferably at least about 50 ksi (340 MPa), more highly preferably at least about 75 ksi (510 MPa), and most preferably at least about 100 ksi (690 MPa).
• the film preferably meets those strength and modulus requirements in at least two directions that are parallel to the plane of the film and perpendicular to each other.
• the film more preferably meets those strength and modulus requirements in essentially all directions that are parallel to the plane of the film. The strength and modulus are sometimes less perpendicular to the plane of the film.
• the film preferably has no yield point - no point at which stress on the film irreversibly stretches the film from its desired shape without tearing. Its elongation to break is preferably between 1 and 2 percent.
• the film may be cut into any form that is useful for a magnetic media substrate. It is preferably formed into a tape or a disc.
• the thickness of the substrate is preferably minimized, but the substrate must be at least thick enough to substantially retain its shape under the ordinary stresses that it faces when it is used.
• the substrate is usually between 0.1 and 1000 ⁇ m thick. It is preferably no more than about 200 ⁇ m thick, more preferably no more than about 100 ⁇ m thick, more highly preferably no more than about 25 ⁇ m thick and most preferably no more than about 10 ⁇ m thick. It is preferably at least about 0.5 ⁇ m thick and more preferably at least about 1 ⁇ m thick.
• the other dimensions of the substrate are governed by practical considerations relating to the device that it is to be used for. For instance, most magnetic recording tape substrates are between 4 mm and 50 mm wide, but the tape may be wider or narrower if desired.
• the optimum length of the tape substrate is related to the desired recording speed and recording time. For instance, it may be any desired length from 1 meter to greater than 10,000 meters.
• Most magnetic discs are between 35 mm and 135 mm in diameter, but the disc may be larger or smaller if desired.
• the substrate When the substrate is in the form of a tape, then its average tensile modulus across the width of the film is preferably higher than its average tensile modulus along the length of the film.
• the higher tensile modulus along the width can help the tape to lay flatter.
• Such a substrate can be made by mechanically stretching the dope film in the transverse direction before coagulation, so that the resulting polymer film has a higher strength in the transverse direction.
• the film can then be slit longitudinally into suitable tapes.
• the tensile modulus be about uniform in all directions along the plane of the film.
• the variation of tensile modulus in the substrate is preferably no more than about 20 percent, more preferably no more than about 10 percent and most preferably no more than about 5 percent.
• the tensile modulus of the film is high enough, then the need for a uniform tensile modulus is less, because the substrate will not stretch significantly out of roundness in any case.
• a magnetizable layer adheres to at least one face of the substrate. Magnetizable layers may optionally adhere to both faces.
• the magnetizable layer contains either a continuous thin film of magnetizable material, or a magnetizable particulate and a binder.
• the magnetizable particulate may be any particulate material that can be magnetized to provide a readable medium. Examples of suitable magnetizable materials are described previously and in Sharrock, "Particulat'e Recording Media,” MRS Bulletin Volume XV, No.3 at 53-61 (Materials Research Society March 1990).
• the magnetizable particulate is preferably cobalt gamma iron oxide or barium ferrite. It is most preferably barium ferrite.
• the particle size is limited by practical considerations, such as ease of handling. It is usually between 0.25 ⁇ m and 2 ⁇ m, measured along the long axis of the particulate.
• the particles may be coated with a dispersant, a high molecular weight compound, or another material to prevent agglomeration of the particles on the substrate.
• a dispersant a high molecular weight compound
• suitable coatings are described in Nakayama et al., Magnetic Powders With Improved Dispersibility, U.S. Patent 4,619,861 (October 28, 1986).
• Particles are typically held on the substrate by a binder.
• the binder should be flexible, and adhere to the particles and substrate.
• suitable binders include urethanes, acrylics and epoxy resins.
• the thickness of the binder and particles on the tape is governed by practical considerations. It is usually at least about 500 A thick. It is usually no more than about 40,000 A and is preferably no more than about 4000 A, although the magnetizable layer may be thicker or thinner if desired.
• the binder and particles may be applied to the substrate by known methods, such as by slot-die coating or spin-coating.
• the binder and particulate material may be dispersed in an organic solvent, coated on the substrate, and deposited by removing the solvent, as described in Sharrock, "Particulate Recording Media,” MRS Bulletin Volume XV, No. 3 at 53-61 (Materials Research Society March 1990).
• the magnetizable layer may alternatively be a thin continuous layer of magnetizable material.
• the magnetizable layer may be, for instance, barium ferrite or a nickel-cobalt oxide alloy.
• the magnetizable layer is preferably as thin as practical, but is usually at least about 100 ⁇ thick. It is preferably no more than about 5000 ⁇ thick, more preferably no more than about 3000 ⁇ thick, and most preferably no more than about 1500 ⁇ thick.
• This layer may be applied as a thin film by conventional methods using an adhesive. However, it is preferably applied directly to the substrate by methods such as sputtering or vapor deposition.
• the polybenzazole substrates of the present invention can withstanding the temperatures needed to deposit materials by ordinary sputtering and vapor deposition (metal evaporation) processes.
• the optimal temperature for depositing the magnetizable layer varies depending upon the magnetizable material that is being deposited. For instance, barium ferrite can be deposited at temperatures below about 300°C, but it is less effective for magnetic recording than barium ferrite that is deposited at a temperature of 300°C or greater. Barium ferrite is preferably sputtered at a temperature of at least about 300°C, more preferably at least about 400°C and most preferably at least about 450°C. Similar temperatures may be used with other magnetizable materials, if desired.
• the temperature is preferably no more than 650°C and more preferably no more than about 550°C.
• the pressure during sputtering is preferably no more than 10 -3 torr (.13 Pa) and more preferably no more than about 10 -4 torr (.013 Pa) and more preferably no more than about 10 -5 torr (.0013 Pa).
• the minimum pressure is not critical. It is governed by practical considerations and is usually no less than 10 -7 torr (.000013 Pa).
• the magnetic medium may optionally further contain a third "overcoat" layer over the magnetizable layer to protect the magnetizable layer and/or smooth the surface of the medium.
• the overcoat layer is usually at least about 250 A thick. It is usually no more than 5000 ⁇ thick.
• the overcoat layer preferably contains materials that are flexible, strong enough to protect the magnetic layer, adhesive on the magnetizable layer, thermally stable and/or have low water uptake. For instance, a carbon layer may be sputtered over a continuous thin magnetizable layer, or aluminum oxide particles and a lubricant such as perflouropolyether may be applied over a particulate and binder layer. Examples of other overcoat layers are described in Kitoo et al., Magnetic Recording Medium Having Organic Protective Overlayer, U.S. Patent 4,529,651 (July 16, 1985).
• the coercivity of the finished magnetic recording medium is preferably at least about 500 Oe, and more preferably at least about 900 Oe, and most preferably at least about 1500 Oe.
• the polybenzazole substrates of the present invention have significant advantages over substrates in the prior art.
• Polybenzazole polymers have high tensile strength and modulus, so that they can be made thin. Additional advantages may also be obtained.
• Many preferred polymers have essentially no yield point up to the point that they tear, so that stresses below the tensile strength frequently will not permanently distort the shape of the substrate.
• Many preferred polybenzazole polymers are essentially non-melting and thermally stable, so that exposure to high temperature, even those suitable for sputtering, does not harm the substrate.
• Barium ferrite can be sputtered directly on the substrate. They can be used in an ordinary manner for magnetic media.
• a film of cis-PBO was made by (1) extruding a dope film from dope containing 14 percent cis-PBO dissolved in polyphosphoric acid that contained about 84 percent P 2 O 5 ; (2) stretching the dope film to three times its length and five times width; (3) coagulating and washing in water and drying in an oven.
• the film thickness was about 0.2 mil (5 ⁇ m).
• the film was heated to a temperature shown in Table I under a pressure of 0.1 mtorr for 30 minutes. It was plasma cleaned at the temperature at a pressure of 0.5 mtorr with a gas composition of 25 percent oxygen and 75 percent argon. The sample was then sputter-coated with barium ferrite at a pressure of 0.5 mtorr under the temperature and for the time shown in Table I until the coating thickness is as shown in Table I.
• Sample 1-1 500 8.5 1000 Sample 1-1 has a coercivity of 970 to 995 Oe as measured by a vibrating sample magnetometer which was commercially available from Digital Measurement Systems.
• a film as described in Example 1 was sputter-coated with a layer of barium ferrite 2000 to 4000 ⁇ thick at a temperature of 450°C to 500°C and a pressure 10 -6 torr.
• the film had a coercivity of 1350 Oe, as measure by the equipment in Example 1.
• a 3000 ⁇ thick coating containing barium ferrite particulate and an epoxy resin binder wasapplied to a 0.8 mil (20 ⁇ m) thick tape containing PBO polymer tape by spin coating the particulate and binder on the tape and curing the epoxy resin.
• the tape had a coercivity of 1000 Oe as measured by the equipment in Example 1.
• a PBO tape as described in Claim 1 was metallized by contacting it with evaporated cobalt and 10 -5 torr oxygen for a period of time sufficient to deposit a layer about 2000 ⁇ thick on average.
• the metallized film had a coercivity of 1677 Oe parallel to the deposition direction and 865 Oe perpendicular to the deposition direction.

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• 1992
  • 1992-07-09 TW TW081105450A patent/TW216460B/zh active
  • 1992-07-09 TW TW081105449A patent/TW240311B/zh active
• 1993
  • 1993-03-11 JP JP5516615A patent/JPH07504291A/ja active Pending
  • 1993-03-11 EP EP93907411A patent/EP0632921A1/en not_active Withdrawn
  • 1993-03-11 WO PCT/US1993/002206 patent/WO1993019461A1/en not_active Application Discontinuation
  • 1993-03-11 WO PCT/US1993/002207 patent/WO1993019462A1/en active Application Filing
  • 1993-03-11 CA CA002132710A patent/CA2132710A1/en not_active Abandoned
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• 1994
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