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
  • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
  • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
• • 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
  • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers

Definitions

• This invention relates to the production of magnetic recording structures, especially tapes, in which a layer of magnetizable particles of reduced thickness, preferably only one or two particles thick, is applied to a nonmagnetizable substrate.
• magnetizable particles a liquid coating composition which has been pigmented with particles having the capacity to retain a magnetic orientation, referred to hereinafter as magnetizable particles, is applied to an appropriate nonmagnetizable substrate.
• the pigmented coating is then baked to solidify the coating and fix the magnetizable particles in place within the coating.
• the magnetizable particles are used in admixture with a nonmagnetizable binder (which may be thermoplastic or thermosetting) and a volatile solvent to provide a pigmented coating composition which is applied as a thin coating upon the substrate which is then baked to remove the solvent and to cure the binder if it is curable.
• a substrate is first coated w th a liquid coating composition which is substantially free of magnetizable particles and which provides a tacky surface having the capacity to bond to magnetizable particles applied to the tacky surface thereof.
• Magnetizable particles are then applied to the exposed tacky surface of the applied coating, and this may be done by dusting a dry powder or by spraying on a suspension of the particles in a volatile organic solvent or by transferring dry powder that has previously been coated on a smooth surface that will readily release the dry pigment.
• the coated substrate with the particles thereon is then solidified, as by heating or exposure to radiation when the binder is radiation-curable.
• the substrate is normally nonmagnetizable, as when Mylar is used, but any substrate can be used. If orientation of the magnetizable particles is desired, the coated substrate with the particles adhered to its exposed surface is passed through a magnetic field, which may be vertical or horizontal, as desired, and the coating is preferably solidified while the coating is within this magnetic field.
• This expedient of solidifying the coating while it is within the magnetic field is the subject of a commonly owned application, or if it is not used, the particles can be oriented and then transferred to the tacky surface.
• the objective of this invention is to adhere to the binder-coated substrate as close to a single layer of particles as possible. Excess particles which are not bound by the binder may be blown or brushed off prior to or after solidification of the wet coating or thereafter.
• the applied magnetizable particles are concentrated by being confined to the surface of the previously applied coating and are prevented from becoming dispersed in that coating.
• the process of this invention produces a magnetic recording structure having a higher recording density and improved recording characteristics because the magnetizable particles are more densely packed and confined to a thinner • layer. More particularly, many of the magnetizable particles are only partially embedded in the upper surface of the layer of nonmagnetizable resin, and this structure distinguishes the products of this invention from the magnetic recording structures previously available. This also provides a desirable economy.
• the final structure may be overcoated to protect the magnetizable particles, but this is not essential for in some systems, there is no contact between the recording head and the upper surface of the layer which is intended to receive the magnetic image.
• magnetizable particles are not an aspect of this invention. These are illustrated by acicular particles of pigment grade which may be modified with cobalt oxide. The coercivity of these particles is a variable, and the appropriate selection of this factor is known in the art.
• U. S. Patent No. 4,246,316 contains an extensive disclosure of suitable magnetizable particles.
• the preferred substrate is commonly biaxially oriented polyethylene terephthalate when that substrate is to form part of the final magnetic recording structure, but the choice of the nonmagnetizable substrate and its thickness are known to the art.
• temporary substrates can be used, such as polytetrafluorethylene, commercially available under the name Teflon, when laminating processes are employed, as will be illustrated in the examples herein.
• Teflon facilitates removal of the temporary substrate after the resin layer with the magnetizable pigment bonded to one surface thereof has been removed.
• Any liquid coating composition which will adhere to the substrate and which will provide a tacky surface may be employed. Since conventional thermoplastic and thermosetting binders are nonmagnetizable, any of these may be used, normal application being from a solution in a volatile organic solvent. However, and since all that is desired is adhesion to the substrate and an adherent surface, one may also employ aqueous coatings,. including aqueous latices of thermoplastic emulsion copolymers.
• Polyacrylates are particularly preferred and will be illustrated herein. Electron beam radiation is preferred for curing these polyacrylate coating compositions since the pigment which is associated with the predeposited layer of
• liquid solvent solution coatings which contain at least one viscous nonpourable liquid to normally solid polyethylenically unsaturated compound having at least 2.5 repeating units (preferably at least 4) held together by linkages selected from the group consisting of urethane groups, urea groups, thiocarbamate groups, and mixtures thereof, and there is an average of one ethylenically unsaturated group per from 750 to 10,000 units of molecular weight.
• the repeating units preferably have a molecular weight in the range of 60-2000, more preferably from 200-1500, and the groups containing the ethylenic unsaturation are not counted as repeating units.
• the liquid vehicle has low viscosity to enable coating, and the status of the unsaturated compound is noted at 25°C.
• the solvent may be ethylenically unsaturated, and hence reactive during the electron beam cure, or it can be nonreactive, e.g., an ordinary organic solvent. If the wet-coated substrate contains a volatile nonreactive solvent, this volatile solvent is removed, as by vaporization at room or slightly elevated temperature so that the surface is tacky. After the process of this invention has been carried out, the coating with the layer of magnetizable particles adhered thereto is exposed to electron beam radiation to convert the unsaturated compound into a solid thermoset coating having a layer of magnetizable particles confined to
• the polyethylenical-ly unsaturated compounds are formed to contain a plurality of repeating units which are held together by certain selected groups, as previously set forth.
• a diol such as 1,4-butane diol
• a diisocyanate like isophorone diisocyanate
• linear oligomer which may be either isocyanate-terminated or hydroxy terminated, depending upon which functional group is in excess.
• proportions e.g., by using a 3:2 or 4:3 equivalent ratio between the functional groups which are interreacted, several repeating groups will be formed, and they will be linked by urethane groups.
• linking groups in the oligomer which is formed will contain some urea groups and some urethane groups.
• dimercaptan like 1,6-hexane dimercaptan
• the product will now be an oligomer in which the repeating units are thiocarbamate groups.
• OMPI * -7- are illustrated by trimethylol propane or pentaerythritol. Triisocyanates, like the biuret of hexamethylene diisocyante, are also useful.
• the plurality of linkages of the type noted provides the oligomer with improved toughness, and the many variation which are permissible will be evident to those skilled in the art and are illustrated more fully in commonly owned application serial No. 473,544 filed Mar. 9, 1983.
• the oligomers described above are terminated with unsaturated groups, preferably with acrylate groups. This is easily done by using either hydroxyethyl acrylate or its reaction product with one molar proportion of a diisocyanate, like isophorone diisocyanate, to provide an unsaturated monoisocyanate.
• the hydroxyethyl acrylate is selected as the reactant when the oligomer is terminated with isocyanate functionality.
• the raonoisocyante is selected when the oligomer is terminated with isocyante-reactive groups.
• oligomers are diluted to coating viscosity by the inclusion of reactive solvents, like trimethylol propane triacrylate, or by the presence of a monoethylenically unsaturated monomer, like N-vinyl pyrrolidone, or by the presence of a volatile nonreactive solvent, like methyl ethyl ketone.
• reactive solvents like trimethylol propane triacrylate
• a monoethylenically unsaturated monomer like N-vinyl pyrrolidone
• a volatile nonreactive solvent like methyl ethyl ketone
• the radiation-curable resin employed is of the type described above, and is a mixture of an ethylenically unsaturated polymer prepared from 4, '-methylene bis phenyl isocyante, poly tetramethylene glycol of average molecular weight 650 and 2-hydroxyethyl acrylate at a mole ratio of 6 to 5 to 2 (50% solution in methyl ethyl ketone), 2-isophorone diisocyanate trimer-2-hydroxyethyl acrylate adduct (60% solution in methyl ethyl ketone) and N-vinyl pyrrolidone at a 70/20/10 weight ratio based on solids.
• Example 1 A thin layer of magnetic pigment is deposited on a tacky, uncured but curable resin coated onto a polyethylene terephthalate substrate in the following manner.
• the resin coated subtrate with magnetic pigment on the surface was then passed through an electron beam processor and cured using a dose of 10 megarads
• the resulting coated sheet was then burnished with burnishing paper to remove excess pigment from the surface and to smooth and polish the surface.
• the result was a magnetic media that had a very thin, highly concentrated layer of magnetic oxide on the surface, approximately 2,000 - 4,000 angstroms thick.
• the particles were random oriented.
• Example 2 The same system in which the magnetic pigment was electrostatically sprayed on the surface of the uncured resin, resulted in a pigment surface of between 6,000 and 20,000 angstroms thick, with the particles oriented in the vertical direction.
• Example 2 The same system in which the magnetic pigment was electrostatically sprayed on the surface of the uncured resin, resulted in a pigment surface of between 6,000 and 20,000 angstroms thick, with the particles oriented in the vertical direction.
• the laminated mass was then cured in an electron beam processor using a dose of 10 megarads.
• the Teflon film was peeled away, leaving a film constituted by a polyethylene terephthalate base coated with a film of cured resin having a thin layer of magnetic oxide embedded on the surface of the cured resin.
• the pigmented surface was then burnished with paper to remove the excess unadhered pigment and to smooth and polish the surface.
• a thin layer of magnetic oxide that had been treated with Dow Corning 2-6032 was coated by means of a drawdown bar onto a smooth, chrome-plated sheet. This pigment-coated sheet was then passed through a curtain coater and a 1 mil thick layer of pigment-free resin was laid down over the thin layer of dry pigment.
• a polyethylene terephthalate sheet can be laminated to the uncured resin surface, or the coated chrome sheet can be processed as is.
• the coated sheet is then put into an electron beam processor and exposed to a dose of 10 megarads.
• the cured coating is then.removed from the chrome base and burnished with paper to remove excess magnetic pigment and to smooth the surface.
• the resulting film is a magnetic media with a thin (2,000 angstrom), highly concentrated layer of magnetic pigment on the surface.

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• Manufacturing Of Magnetic Record Carriers (AREA)
• Paints Or Removers (AREA)

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• 1984
  • 1984-08-30 EP EP19840903332 patent/EP0153949A1/de not_active Withdrawn
  • 1984-08-30 WO PCT/US1984/001381 patent/WO1985001147A1/en unknown

Non-Patent Citations (1)

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