Hajime Fukke

Effect of polymer adsorbed layer on magnetic particle dispersion

Experimental and theoretical investigations of dispersion properties of magnetic particles (acicular gamma -Fe/sub 2/O/sub 3/) with an adsorbed epoxy-resin layer are presented. The adsorbed polymer amount was 20-110 mg/g and the adsorbed layer thickness was 6-22 nm, depending on the preparation conditions. Dispersion of gamma -Fe/sub 2/O/sub 3/ particles was evaluated by the sedimentation rate and surface roughness of the coated film. It was clarified that dispersion was improved with increasing adsorption, increasing solvent/epoxy-resin solubility, and decreasing gamma -Fe/sub 2/O/sub 3/ particle size. Interaction energy, consisting of magnetic attraction, van der Waals attraction, and steric repulsion of the adsorbed layer between two cylindrical magnetic particles, was calculated. The interaction energy curves, which vary with the distance between two particles, had primary minimum, maximum, and secondary minimum. The maximum energy and the secondary minimum energy were strongly related to dispersion stability. Experimental results are explained by the energy curve shapes. >

Polymer adsorbed layer on an iron oxide particle surface in iron oxide/epoxy resin/solvent dispersion

Abstract Dispersion of magnetic γ-Fe2O3 particles which have an adsorbed epoxy-resin layer is investigated. γ-Fe2O3 particles which have various amounts of adsorbed polymer are prepared, and some parameters, which characterize the adsorbed layer, are measured. When the amount of adsorbed polymer increases, the thickness of the adsorbed layer also increases, but the polymer concentration of the adsorbed layer is kept constant in accordance with the polymer/solvent solubility. It is found that a low sedimentation rate, i.e., good dispersion stability, is caused by large amounts of the adsorbed polymer.

Polymer adsorption on a magnetic particle in a dispersion system

Abstract A magnetic particle dispersion was prepared by mixing the magnetic γ - Fe 2 O 3 particles or barium-ferrite particles and epoxy resin with solvent. The relationship between the mixing conditions and the adsorbed amount of the epoxy resin on the particle surface was investigated. It became clear that the polymer adsorption occurring during the mixing process required both large mechanical shear and high temperature. The large mechanical shear was necessary to break the coagulation of the particles and high temperature was necessary to cause chemical reaction between the polymer and the particle surface. The adsorbed polymer improved dispersibility of the particles in the dispersion, which was confirmed by transmission electron micrograph, viscosity measurement and surface roughness measurement of the coated films made from the dispersions.

The effect of adsorbed polymer molecular weight on magnetic particle dispersibility

Abstract Dispersibility of acicular magnetic particles which have an adsorbed epoxy resin layer around them is investigated. The relationship between resin molecular weight and adsorbed layer characteristics, e.g., adsorbed resin amount, adsorbed solvent amount, adsorbed layer thickness, is determined. A thick adsorbed layer which contains large amounts of solvent results from the large molecular weight of the epoxy resin. Such a thick adsorbed layer plays an important role in stabilizing dispersion because of its steric repulsion effect. This steric repulsion effect can be estimated by the interaction energy calculation between two particles. The resin molecular weight dependence of dispersibility can also be predicted by the calculation, which supports the experimental results.

Effect of Co- gamma Fe/sub 2/O/sub 3/ particle-size on high density rigid disks

The effects of particle size on the read/write characteristics of Co- gamma Fe/sub 2/O/sub 3/ particulate rigid disks are investigated. Smaller particle size reduces PW/sub 50/, the half-width of an isolated pulse wave, as well as disk noise. The transition region widens as the particle size increases. The change in the transition region seems to originate from the particle size itself, rather than from any inhomogeneity of the magnetic properties. The thickness dependence of the read/write characteristics of ultrathin coated disks using fine Co- gamma Fe/sub 2/O/sub 3/ particles was also investigated. In a 0.12- mu m-thick disk, D/sub 50/ is 36.5 kFCI at 0.20- mu m head flying height. >

Method for magnetic orientation of magnetic recording medium using Meissner effect of high Tc superconductor

A method for magnetic orientation of a magnetic recording medium using Meissner effect of a superconductor and a system therefor and a magnetic recording medium produced thereby. The magnetic particles of plate hexagonal barium ferrite in the magnetic coating are allowed to orient in the longitudinal direction thereof so that a magnetic recording medium having a magnetic orientation in such direction with the magnetic particles can be obtained.

Effects of particle size on read/write properties of Ba ferrite and Co-γFe2O3 coated media

Abstract The effects of particle size on the read/write properties in Ba ferrite and Co-γFe 2 O 3 particulate rigid disks are described and compared. We have already reported that the half-width of isolated pulses (PW 50 ) in Co-γFe 2 O 3 disks decreased as the particle size became smaller. In Ba ferrite disks, however, PW 50 does not decrease as the particle size becomes smaller, that is, as the specific surface area (SSA) increases. The SSA independence is caused by the fact that the thinness of the Ba ferrite particles along the easy axis of magnetization, the thickness direction, is much thinner than that along the transition length. The PW 50 of Ba ferrite disks is smaller than that of Co-γFe 2 O 3 disks. The small PW 50 values of the Ba ferrite disks, compared with those of Co-γFe 2 O 3 disks, can be explained by the small SFD values and the thinness of Ba ferrite particles. The decreasing slope of the signal-recorded noise with increasing recording density in Ba ferrite disks is smaller than that in Co-γFe 2 O 3 disks. The peak height or dip depth of the reverse dc-erase noise in Ba ferrite disks is also smaller than dip depth in Co-γFe 2 O 3 disks.

Agglomerates and media-noise of ultra-thin coated rigid disks☆

Abstract This paper discusses the media-noise properties of ultra-thin coated rigid disks and their origin. The ultra-thin coated rigid disks using Co-γFe 2 O 3 fine particles were obtained after spin-coating Al-substrates with magnetic paints. Thickness values between 0.12 and 0.33 μm were obtained after controlled spin-coating. After removing high protrusions on disk-surfaces, the read/write properties of ultra-thin coated rigid disks were investigated using a MIG head. The media-noise properties of the ultra-thin coated disks were compared with those of a conventional particulate disk and a thin film disk. The signal-recorded noises, the dc-erase noise, and the reverse dc-erase (RDC) noises were measured. A peculiar recording density dependence for the signal-recorded noise was found. The signal-recorded noise of the ultra-thin coated disks has a maximum value at a density of 17.5 kFCI. In the region below 17.5 kFCI, the signal-recorded noise increases like a thin film disk as the recording density increases. In the region larger than 17.5 kFCI, the signal-recorded noise decreases like a conventional particulate disk as the recording density increases from 17.5 kFCI. This peculiar dependence is caused by cohered agglomerates which consist of randomly oriented magnetic particles in the magnetic layer of the ultra-thin coated disks.